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Factorising Complex
    Expressions
Factorising Complex
       Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
Factorising Complex
       Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
Every polynomial of degree n can be;
Factorising Complex
       Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
Every polynomial of degree n can be;
• factorised as a mixture of quadratic and linear factors over the
  real field
Factorising Complex
       Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
Every polynomial of degree n can be;
• factorised as a mixture of quadratic and linear factors over the
  real field
• factorised to n linear factors over the complex field
Factorising Complex
       Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
Every polynomial of degree n can be;
• factorised as a mixture of quadratic and linear factors over the
  real field
• factorised to n linear factors over the complex field
NOTE: odd ordered polynomials must have a real root
Factorising Complex
         Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
 Every polynomial of degree n can be;
 • factorised as a mixture of quadratic and linear factors over the
   real field
 • factorised to n linear factors over the complex field
 NOTE: odd ordered polynomials must have a real root

e.g . i  x 2  2 x  2
Factorising Complex
         Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
 Every polynomial of degree n can be;
 • factorised as a mixture of quadratic and linear factors over the
   real field
 • factorised to n linear factors over the complex field
 NOTE: odd ordered polynomials must have a real root

e.g . i  x 2  2 x  2   x  12  1
Factorising Complex
         Expressions
If a polynomial’s coefficients are all real then the roots will appear
in complex conjugate pairs.
 Every polynomial of degree n can be;
 • factorised as a mixture of quadratic and linear factors over the
   real field
 • factorised to n linear factors over the complex field
 NOTE: odd ordered polynomials must have a real root

e.g . i  x 2  2 x  2   x  12  1
                          x  1  i  x  1  i 
ii  z 4  z 2  12  0
ii  z 4  z 2  12  0
    z   2
              3z 2  4   0
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                 factorised over Real numbers
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
          z   3 or z  2i
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
         z   3 or z  2i
iii  Factorise 2 x 3  3x 2  8 x  5
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
          z   3 or z  2i
iii  Factorise 2 x 3  3x 2  8 x  5
       as it is a cubic it must have a real factor
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
          z   3 or z  2i
iii  Factorise 2 x 3  3x 2  8 x  5
       as it is a cubic it must have a real factor
                       3           2

 P    2    3    8    5
        1          1           1          1
                                   
    2  2                2          2
                 1 3
               45
                 4 4
            0
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
          z   3 or z  2i
iii  Factorise 2 x 3  3x 2  8 x  5
       as it is a cubic it must have a real factor
                       3           2

 P    2    3    8    5
        1           1           1           1
                                    
    2  2                 2          2
                 1 3
               45
                 4 4
            0
 2 x 3  3 x 2  8 x  5  2 x  1x 2  2 x  5
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
          z   3 or z  2i
iii  Factorise 2 x 3  3x 2  8 x  5
       as it is a cubic it must have a real factor
                       3           2

 P    2    3    8    5
        1           1           1           1
                                    
    2  2                 2          2
                 1 3
               45
                 4 4
            0
 2 x 3  3 x 2  8 x  5  2 x  1x 2  2 x  5
                                     
                            2 x  1  x  1  4
                                             2
                                                      
ii  z 4  z 2  12  0
    z  3z  4  0
      2        2


    z  3 z  3z  4  0
                           2
                                           factorised over Real numbers
   z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
          z   3 or z  2i
iii  Factorise 2 x 3  3x 2  8 x  5
       as it is a cubic it must have a real factor
                       3           2

 P    2    3    8    5
        1           1           1           1
                                    
    2  2                 2          2
                 1 3
               45
                 4 4
            0
 2 x 3  3 x 2  8 x  5  2 x  1x 2  2 x  5
                                       
                            2 x  1  x  1  4
                                               2
                                                     
                            2 x  1 x  1  2i  x  1  2i 
iv  z 5  z 4  z 3  z 2  z  1  0
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
    And z 6  1  0 has solutions;
             2 k 
    z  cis        k  0, 1, 2,3
             6 
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
    And z 6  1  0 has solutions;
             2 k 
    z  cis        k  0, 1, 2,3
             6 
    z5  z4  z3  z2 1  0
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
    And z 6  1  0 has solutions;
             2 k 
    z  cis        k  0, 1, 2,3
             6 
    z5  z4  z3  z2 1  0

   z  1z 5  z 4  z 3  z 2  1
                                      0
                 z  1
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
    And z 6  1  0 has solutions;
             2 k 
    z  cis        k  0, 1, 2,3
             6 
    z5  z4  z3  z2 1  0

   z  1z 5  z 4  z 3  z 2  1
                                      0
                 z  1
               z 6  1  0, z  1
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
    And z 6  1  0 has solutions;
             2 k 
    z  cis        k  0, 1, 2,3
             6 
    z5  z4  z3  z2 1  0

   z  1z 5  z 4  z 3  z 2  1
                                      0
                 z  1
            z 6  1  0, z  1
                         2          2
  z  cis , cis  , cis        , cis     , cis
         3         3        3           3
iv  z 5  z 4  z 3  z 2  z  1  0
      Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
    And z 6  1  0 has solutions;
             2 k 
    z  cis        k  0, 1, 2,3
             6 
    z5  z4  z3  z2 1  0

   z  1z 5  z 4  z 3  z 2  1
                                      0
                 z  1
            z 6  1  0, z  1
                         2          2
  z  cis , cis  , cis        , cis      , cis
         3         3        3           3
      1    3 1         3      1      3      1     3
  z         i,        i,          i,         i, 1
      2 2 2 2                 2 2           2 2
v 1996 HSC
                2          2
    Let   cos      i sin
                 9           9
a) Show that  k is a solution of z 9  1  0, where k is an integer
v 1996 HSC
                2          2
    Let   cos      i sin
                 9           9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
v 1996 HSC
                 2          2
    Let   cos       i sin
                   9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
             2k 
    z  cis           k  0,1,2,3,4,5,6,7,8
             9  
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
    z  k
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
    z  k
b) Prove that    2   3   4   5   6   7   8  1
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
    z  k
b) Prove that    2   3   4   5   6   7   8  1
                  z9 1  0
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
    z  k
b) Prove that    2   3   4   5   6   7   8  1
                  z9 1  0
   1     2   3   4   5   6   7   8  0
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
    z  k
b) Prove that    2   3   4   5   6   7   8  1
                  z9 1  0
   1     2   3   4   5   6   7   8  0 sum of roots 
v 1996 HSC
                   2          2
    Let   cos         i sin
                     9          9
a) Show that  k is a solution of z 9  1  0, where k is an integer
   z9  1
              2k 
     z  cis            k  0,1,2,3,4,5,6,7,8
              9  
              2
                    k

    z  cis 
                 
               9 
    z  k
b) Prove that    2   3   4   5   6   7   8  1
                  z9 1  0
   1     2   3   4   5   6   7   8  0 sum of roots 
         2   3   4   5   6   7   8  1
       2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B 
 sin A  sin B  2sin        cos       
                        2          2 
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B    (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2       cos half diff)
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B    (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2       cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos                  
                        2   2 
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B    (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2       cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                              (2 cos half sum
                                        
                        2   2                cos half diff)
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B    (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2       cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                              (2 cos half sum
                                        
                        2   2                cos half diff)

                       A B   A B 
cos A  cos B  2sin        sin   
                        2   2 
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B      (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2         cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                                (2 cos half sum
                                        
                        2   2                  cos half diff)

                       A B   A B        (minus 2 sine half sum
cos A  cos B  2sin        sin   
                        2   2                 sine half diff)
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B            (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2               cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                                      (2 cos half sum
                                        
                        2   2                        cos half diff)

                       A B   A B             (minus 2 sine half sum
cos A  cos B  2sin        sin   
                        2   2                      sine half diff)
             2   3   4   5   6   7   8  1
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B            (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2               cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                                      (2 cos half sum
                                        
                        2   2                        cos half diff)

                       A B   A B             (minus 2 sine half sum
cos A  cos B  2sin        sin   
                        2   2                      sine half diff)
             2   3   4   5   6   7   8  1
 roots appear in conjugate pairs
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B            (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2               cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                                      (2 cos half sum
                                        
                        2   2                        cos half diff)

                       A B   A B             (minus 2 sine half sum
cos A  cos B  2sin        sin   
                        2   2                      sine half diff)
             2   3   4   5   6   7   8  1
 roots appear in conjugate pairs
                 2         4        6        8
           2cos       2cos     2cos     2cos     1
                  9          9         9         9
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B            (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2               cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                                      (2 cos half sum
                                        
                        2   2                        cos half diff)

                       A B   A B             (minus 2 sine half sum
cos A  cos B  2sin        sin   
                        2   2                      sine half diff)
             2   3   4   5   6   7   8  1
 roots appear in conjugate pairs
                 2         4           6        8
           2cos       2cos       2cos      2cos      1
                   9          9           9         9
                  2       4         6       8     1
             cos      cos       cos     cos    
                   9        9          9        9     2
  2   4 1
c) Hence show that cos cos cos   
                      9    9    9 8
                       A B       A B            (2 sine half sum
 sin A  sin B  2sin        cos       
                        2          2               cos half diff)
                      A  B  cos A  B 
cos A  cos B  2 cos
                                                      (2 cos half sum
                                        
                        2   2                        cos half diff)

                       A B   A B             (minus 2 sine half sum
cos A  cos B  2sin        sin   
                        2   2                      sine half diff)
             2   3   4   5   6   7   8  1
 roots appear in conjugate pairs
                 2         4           6         8
           2cos       2cos       2cos       2cos      1
                   9          9           9          9
                  2       4         6        8     1
             cos      cos       cos      cos    
                   9        9          9         9     2
                      3                7           1
                 2cos cos  2cos             cos  
                       9      9           9      9     2
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
            3       7      1
    cos  cos     cos      
       9      9        9      4
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
            3       7      1
    cos  cos     cos      
       9      9        9      4
             5   2    1
     cos  2cos cos    
        9      9    9    4
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
            3       7         1
    cos  cos     cos         
       9      9        9         4
             5   2    1
     cos  2cos cos    
        9      9    9    4
                      2     5    1
       cos       cos      cos    
             9          9      9    8
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
            3       7          1
    cos  cos     cos          
       9      9        9          4
             5   2    1
     cos  2cos cos    
        9      9    9    4
                      2     5    1
       cos       cos      cos    
             9          9      9    8
                        5         4
          But cos            cos
                         9          9
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
            3       7         1
    cos  cos     cos         
       9      9        9         4
             5   2    1
     cos  2cos cos    
        9      9    9    4
                      2     5    1
       cos       cos      cos    
             9          9      9    8
                 5          4
          But cos      cos
                  9           9
               2      4      1
       cos cos     cos    
           9     9       9      8
3         7        1
2cos cos  2cos    cos  
     9  9        9    9    2
            3       7         1
    cos  cos     cos         
       9      9        9         4
             5   2    1
     cos  2cos cos    
        9      9    9    4
                      2     5    1
       cos       cos      cos    
             9          9      9    8
                 5          4
          But cos      cos
                  9           9
               2      4      1
       cos cos     cos    
           9     9       9      8
               2      4 1
        cos cos     cos     
            9    9       9 8
OR
z9 1
  z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5 
OR
z9 1
  z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5 

                       2                  4      
  z  1  z 2  2cos    z  1 z 2  2cos    z  1
                        9                   9      
                  2        6         2        8       
                  z  2cos     z  1 z  2cos      z  1
                            9                   9       
OR
z9 1
  z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5 

                       2                  4      
  z  1  z 2  2cos    z  1 z 2  2cos    z  1
                        9                   9      
                  2        6         2        8       
                  z  2cos     z  1 z  2cos      z  1
                            9                   9       
            2          2          2         4      
  z  1  z  2cos       z  1 z  2cos       z  1
                        9                     9      
                                          8      
                z 2  z  1  z 2  2cos
                                           9
                                              z  1
                                                   
OR
z9 1
  z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5 

                       2                  4      
  z  1  z 2  2cos    z  1 z 2  2cos    z  1
                        9                   9      
                  2        6         2        8       
                  z  2cos     z  1 z  2cos      z  1
                            9                   9       
            2          2          2         4      
  z  1  z  2cos       z  1 z  2cos       z  1
                        9                     9      
                                          8      
                z 2  z  1  z 2  2cos
                                           9
                                              z  1
                                                   
  Let z  i
OR
z9 1
  z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5 

                       2                  4      
  z  1  z 2  2cos    z  1 z 2  2cos    z  1
                        9                   9      
                  2        6         2        8       
                  z  2cos     z  1 z  2cos      z  1
                            9                   9       
            2          2          2         4      
  z  1  z  2cos       z  1 z  2cos       z  1
                        9                     9      
                                          8      
                z 2  z  1  z 2  2cos
                                           9
                                              z  1
                                                   
  Let z  i
                                 2            4                    8    
       i 9  1   i  1  2cos      i  2cos       i   i   2cos      i
                                  9             9                     9    
       2            4                   8    
i  1   i  1  2cos
9
                              i  2cos      i   i   2cos      i
                         9             9                    9    
       2            4                   8    
i  1   i  1  2cos
9
                              i  2cos      i   i   2cos      i
                         9             9                    9    
                           2       4      8 
 i  1  i  i  1  2cos
          4
                                2cos     2cos 
                            9        9       9 
       2            4                   8    
i  1   i  1  2cos
9
                              i  2cos      i   i   2cos      i
                         9             9                    9    
                           2       4      8 
 i  1  i  i  1  2cos
          4
                                2cos     2cos 
                            9        9       9 
               2       4     8
   1  8cos       cos     cos
                9        9      9
       2            4                   8    
i  1   i  1  2cos
9
                              i  2cos      i   i   2cos      i
                         9             9                    9    
                           2        4      8 
 i  1  i  i  1  2cos
          4
                                 2cos     2cos 
                            9         9       9 
               2       4      8
   1  8cos       cos     cos
                9        9       9
               2       4        
   1  8cos       cos       cos 
                9        9        9
       2            4                   8    
i  1   i  1  2cos
9
                              i  2cos      i   i   2cos      i
                         9             9                    9    
                           2        4      8 
 i  1  i  i  1  2cos
          4
                                 2cos     2cos 
                            9         9       9 
               2       4      8
   1  8cos       cos     cos
                9        9       9
               2       4        
   1  8cos       cos       cos 
                9        9        9
           2     4 1
    cos cos    cos   
       9     9      9 8
       2            4                   8    
i  1   i  1  2cos
9
                              i  2cos      i   i   2cos      i
                         9             9                    9    
                           2        4      8 
 i  1  i  i  1  2cos
          4
                                 2cos     2cos 
                            9         9       9 
               2       4      8
   1  8cos       cos     cos
                9        9       9
               2       4        
   1  8cos       cos       cos 
                9        9        9
           2     4 1
    cos cos    cos   
       9     9      9 8



                   Exercise 4J; 1 to 4, 7ac

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X2 T01 08 factorising complex expressions (2011)

  • 1. Factorising Complex Expressions
  • 2. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs.
  • 3. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be;
  • 4. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be; • factorised as a mixture of quadratic and linear factors over the real field
  • 5. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be; • factorised as a mixture of quadratic and linear factors over the real field • factorised to n linear factors over the complex field
  • 6. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be; • factorised as a mixture of quadratic and linear factors over the real field • factorised to n linear factors over the complex field NOTE: odd ordered polynomials must have a real root
  • 7. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be; • factorised as a mixture of quadratic and linear factors over the real field • factorised to n linear factors over the complex field NOTE: odd ordered polynomials must have a real root e.g . i  x 2  2 x  2
  • 8. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be; • factorised as a mixture of quadratic and linear factors over the real field • factorised to n linear factors over the complex field NOTE: odd ordered polynomials must have a real root e.g . i  x 2  2 x  2   x  12  1
  • 9. Factorising Complex Expressions If a polynomial’s coefficients are all real then the roots will appear in complex conjugate pairs. Every polynomial of degree n can be; • factorised as a mixture of quadratic and linear factors over the real field • factorised to n linear factors over the complex field NOTE: odd ordered polynomials must have a real root e.g . i  x 2  2 x  2   x  12  1   x  1  i  x  1  i 
  • 10. ii  z 4  z 2  12  0
  • 11. ii  z 4  z 2  12  0 z 2  3z 2  4   0
  • 12. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2
  • 13. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers
  • 14. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0
  • 15. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers
  • 16. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i
  • 17. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i iii  Factorise 2 x 3  3x 2  8 x  5
  • 18. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i iii  Factorise 2 x 3  3x 2  8 x  5 as it is a cubic it must have a real factor
  • 19. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i iii  Factorise 2 x 3  3x 2  8 x  5 as it is a cubic it must have a real factor 3 2 P    2    3    8    5 1 1 1 1          2  2  2  2 1 3    45 4 4 0
  • 20. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i iii  Factorise 2 x 3  3x 2  8 x  5 as it is a cubic it must have a real factor 3 2 P    2    3    8    5 1 1 1 1          2  2  2  2 1 3    45 4 4 0  2 x 3  3 x 2  8 x  5  2 x  1x 2  2 x  5
  • 21. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i iii  Factorise 2 x 3  3x 2  8 x  5 as it is a cubic it must have a real factor 3 2 P    2    3    8    5 1 1 1 1          2  2  2  2 1 3    45 4 4 0  2 x 3  3 x 2  8 x  5  2 x  1x 2  2 x  5   2 x  1  x  1  4 2 
  • 22. ii  z 4  z 2  12  0 z  3z  4  0 2 2 z  3 z  3z  4  0 2 factorised over Real numbers z  3 z  3 z  2i  z  2i   0 factorised over Complex numbers z   3 or z  2i iii  Factorise 2 x 3  3x 2  8 x  5 as it is a cubic it must have a real factor 3 2 P    2    3    8    5 1 1 1 1          2  2  2  2 1 3    45 4 4 0  2 x 3  3 x 2  8 x  5  2 x  1x 2  2 x  5   2 x  1  x  1  4 2   2 x  1 x  1  2i  x  1  2i 
  • 23. iv  z 5  z 4  z 3  z 2  z  1  0
  • 24. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1
  • 25. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1 And z 6  1  0 has solutions;  2 k  z  cis   k  0, 1, 2,3  6 
  • 26. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1 And z 6  1  0 has solutions;  2 k  z  cis   k  0, 1, 2,3  6  z5  z4  z3  z2 1  0
  • 27. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1 And z 6  1  0 has solutions;  2 k  z  cis   k  0, 1, 2,3  6  z5  z4  z3  z2 1  0  z  1z 5  z 4  z 3  z 2  1 0  z  1
  • 28. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1 And z 6  1  0 has solutions;  2 k  z  cis   k  0, 1, 2,3  6  z5  z4  z3  z2 1  0  z  1z 5  z 4  z 3  z 2  1 0  z  1 z 6  1  0, z  1
  • 29. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1 And z 6  1  0 has solutions;  2 k  z  cis   k  0, 1, 2,3  6  z5  z4  z3  z2 1  0  z  1z 5  z 4  z 3  z 2  1 0  z  1 z 6  1  0, z  1   2 2 z  cis , cis  , cis , cis  , cis 3 3 3 3
  • 30. iv  z 5  z 4  z 3  z 2  z  1  0 Now z 6  1   z  1z 5  z 4  z 3  z 2  z  1 And z 6  1  0 has solutions;  2 k  z  cis   k  0, 1, 2,3  6  z5  z4  z3  z2 1  0  z  1z 5  z 4  z 3  z 2  1 0  z  1 z 6  1  0, z  1   2 2 z  cis , cis  , cis , cis  , cis 3 3 3 3 1 3 1 3 1 3 1 3 z  i,  i,   i,   i, 1 2 2 2 2 2 2 2 2
  • 31. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer
  • 32. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1
  • 33. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9  
  • 34. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9 
  • 35. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9  z  k
  • 36. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9  z  k b) Prove that    2   3   4   5   6   7   8  1
  • 37. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9  z  k b) Prove that    2   3   4   5   6   7   8  1 z9 1  0
  • 38. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9  z  k b) Prove that    2   3   4   5   6   7   8  1 z9 1  0 1     2   3   4   5   6   7   8  0
  • 39. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9  z  k b) Prove that    2   3   4   5   6   7   8  1 z9 1  0 1     2   3   4   5   6   7   8  0 sum of roots 
  • 40. v 1996 HSC 2 2 Let   cos  i sin 9 9 a) Show that  k is a solution of z 9  1  0, where k is an integer z9  1  2k  z  cis  k  0,1,2,3,4,5,6,7,8  9   2 k z  cis     9  z  k b) Prove that    2   3   4   5   6   7   8  1 z9 1  0 1     2   3   4   5   6   7   8  0 sum of roots     2   3   4   5   6   7   8  1
  • 41. 2 4 1 c) Hence show that cos cos cos  9 9 9 8
  • 42.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  sin A  sin B  2sin   cos    2   2 
  • 43.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)
  • 44.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos     2   2 
  • 45.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)
  • 46.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  cos A  cos B  2sin   sin    2   2 
  • 47.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  (minus 2 sine half sum cos A  cos B  2sin   sin    2   2  sine half diff)
  • 48.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  (minus 2 sine half sum cos A  cos B  2sin   sin    2   2  sine half diff)    2   3   4   5   6   7   8  1
  • 49.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  (minus 2 sine half sum cos A  cos B  2sin   sin    2   2  sine half diff)    2   3   4   5   6   7   8  1 roots appear in conjugate pairs
  • 50.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  (minus 2 sine half sum cos A  cos B  2sin   sin    2   2  sine half diff)    2   3   4   5   6   7   8  1 roots appear in conjugate pairs 2 4 6 8 2cos  2cos  2cos  2cos  1 9 9 9 9
  • 51.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  (minus 2 sine half sum cos A  cos B  2sin   sin    2   2  sine half diff)    2   3   4   5   6   7   8  1 roots appear in conjugate pairs 2 4 6 8 2cos  2cos  2cos  2cos  1 9 9 9 9 2 4 6 8 1 cos  cos  cos  cos  9 9 9 9 2
  • 52.  2 4 1 c) Hence show that cos cos cos  9 9 9 8  A B   A B  (2 sine half sum sin A  sin B  2sin   cos    2   2  cos half diff)  A  B  cos A  B  cos A  cos B  2 cos (2 cos half sum     2   2  cos half diff)  A B   A B  (minus 2 sine half sum cos A  cos B  2sin   sin    2   2  sine half diff)    2   3   4   5   6   7   8  1 roots appear in conjugate pairs 2 4 6 8 2cos  2cos  2cos  2cos  1 9 9 9 9 2 4 6 8 1 cos  cos  cos  cos  9 9 9 9 2 3  7  1 2cos cos  2cos cos   9 9 9 9 2
  • 53. 3  7  1 2cos cos  2cos cos   9 9 9 9 2
  • 54. 3  7  1 2cos cos  2cos cos   9 9 9 9 2  3 7  1 cos  cos  cos  9 9 9  4
  • 55. 3  7  1 2cos cos  2cos cos   9 9 9 9 2  3 7  1 cos  cos  cos  9 9 9  4  5 2  1 cos  2cos cos  9 9 9  4
  • 56. 3  7  1 2cos cos  2cos cos   9 9 9 9 2  3 7  1 cos  cos  cos  9 9 9  4  5 2  1 cos  2cos cos  9 9 9  4  2 5 1 cos cos cos  9 9 9 8
  • 57. 3  7  1 2cos cos  2cos cos   9 9 9 9 2  3 7  1 cos  cos  cos  9 9 9  4  5 2  1 cos  2cos cos  9 9 9  4  2 5 1 cos cos cos  9 9 9 8 5 4 But cos   cos 9 9
  • 58. 3  7  1 2cos cos  2cos cos   9 9 9 9 2  3 7  1 cos  cos  cos  9 9 9  4  5 2  1 cos  2cos cos  9 9 9  4  2 5 1 cos cos cos  9 9 9 8 5 4 But cos   cos 9 9  2 4 1  cos cos cos  9 9 9 8
  • 59. 3  7  1 2cos cos  2cos cos   9 9 9 9 2  3 7  1 cos  cos  cos  9 9 9  4  5 2  1 cos  2cos cos  9 9 9  4  2 5 1 cos cos cos  9 9 9 8 5 4 But cos   cos 9 9  2 4 1  cos cos cos  9 9 9 8  2 4 1 cos cos cos  9 9 9 8
  • 60. OR z9 1   z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5 
  • 61. OR z9 1   z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5   2  4    z  1  z 2  2cos z  1 z 2  2cos z  1  9  9   2 6  2 8   z  2cos z  1 z  2cos z  1  9  9 
  • 62. OR z9 1   z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5   2  4    z  1  z 2  2cos z  1 z 2  2cos z  1  9  9   2 6  2 8   z  2cos z  1 z  2cos z  1  9  9   2 2  2 4    z  1  z  2cos z  1 z  2cos z  1  9  9   8   z 2  z  1  z 2  2cos  9 z  1 
  • 63. OR z9 1   z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5   2  4    z  1  z 2  2cos z  1 z 2  2cos z  1  9  9   2 6  2 8   z  2cos z  1 z  2cos z  1  9  9   2 2  2 4    z  1  z  2cos z  1 z  2cos z  1  9  9   8   z 2  z  1  z 2  2cos  9 z  1  Let z  i
  • 64. OR z9 1   z  1 z     z   8  z   2  z   7  z   3  z   6  z   4  z   5   2  4    z  1  z 2  2cos z  1 z 2  2cos z  1  9  9   2 6  2 8   z  2cos z  1 z  2cos z  1  9  9   2 2  2 4    z  1  z  2cos z  1 z  2cos z  1  9  9   8   z 2  z  1  z 2  2cos  9 z  1  Let z  i  2  4   8  i 9  1   i  1  2cos i  2cos i   i   2cos i  9  9   9 
  • 65. 2  4   8  i  1   i  1  2cos 9 i  2cos i   i   2cos i  9  9   9 
  • 66. 2  4   8  i  1   i  1  2cos 9 i  2cos i   i   2cos i  9  9   9   2  4  8  i  1  i  i  1  2cos 4  2cos  2cos   9  9  9 
  • 67. 2  4   8  i  1   i  1  2cos 9 i  2cos i   i   2cos i  9  9   9   2  4  8  i  1  i  i  1  2cos 4  2cos  2cos   9  9  9  2 4 8 1  8cos cos cos 9 9 9
  • 68. 2  4   8  i  1   i  1  2cos 9 i  2cos i   i   2cos i  9  9   9   2  4  8  i  1  i  i  1  2cos 4  2cos  2cos   9  9  9  2 4 8 1  8cos cos cos 9 9 9 2 4   1  8cos cos   cos  9 9  9
  • 69. 2  4   8  i  1   i  1  2cos 9 i  2cos i   i   2cos i  9  9   9   2  4  8  i  1  i  i  1  2cos 4  2cos  2cos   9  9  9  2 4 8 1  8cos cos cos 9 9 9 2 4   1  8cos cos   cos  9 9  9  2 4 1 cos cos cos  9 9 9 8
  • 70. 2  4   8  i  1   i  1  2cos 9 i  2cos i   i   2cos i  9  9   9   2  4  8  i  1  i  i  1  2cos 4  2cos  2cos   9  9  9  2 4 8 1  8cos cos cos 9 9 9 2 4   1  8cos cos   cos  9 9  9  2 4 1 cos cos cos  9 9 9 8 Exercise 4J; 1 to 4, 7ac