Module 2 exponential functions

Module 2
Exponential Functions
What this module is about
This module is about the roots of exponential equations and zeros of
exponential functions. As you go over this material, you will develop the skills in
finding the roots of exponential equations and the zeros of the exponential
functions using the property of equality for exponential equation and the laws of
exponents.
What you are expected to learn
The module is designed for you to use the laws on exponents to find the
roots of exponential equations and the zeros of exponential functions
How much do you know
1. If 3x
= 34
, what is x?
2. Find x if 2x – 1
= 4.
3. Simplify the expression (4x5
)2
.
4. Express
24
9
4x
2x
−−
−
 
 
− 
without negative exponent.
5. Solve for x in the equation 22
(5x + 1
) = 500
6. What are the values of x in
2x 2x 1
3 9 −
= ?
7. Determine the zeros of the exponential function F(x) = 2x
.
8. Find the zeros of h(x) = 2x - 3
.
9. Where will the graph of y = 1 +
2x 1
1
2
+
 
 
 
cross the x-axis?
10.What value of x will make the function value of y = 32x
– 1 equal to 0?

2
What you will do
Lesson 1
The Property of Equality for Exponential Equation
An exponential equation in one variable is an equation where the
exponent is the variable.
In solving exponential equations, the Property of Equality for Exponential
Equation is used. It is stated as
“If a, b, and c are real numbers and a ≠ 0, then, ab
= ac
if and only if b = c.”
Examples: Solve for the value of the variable that would make the equation
true.
1. 3x
= 35
Since the bases are equal,
x = 5 the exponents must be equal too.
Since the x = 5, then 35
= 35
2. 42y
= 48
Since the bases are equal,
2y = 8 the exponents must be equal too.
y = 4
Since y = 4, then 42y
= 48
42(4)
= 48
48
= 48
3. 72
= 7z – 1
The bases are equal,
2 = z – 1 the exponents must be equal too.
z = 3
Since z = 3, then 72
= 7z – 1
72
= 73 – 1
72
= 72
Try this out
Find the value of the variable that would make each equation true.
Set A
1. 3x
= 39
2. 23y
= 212
3. 52z
= 53

3
4. 8a – 2
= 87
5. 12m + 3
= 120
6. 44b + 1
= 45
7. 75x + 2
= 74x – 1
8. 92(x – 1)
= 93x + 1
9. 64(2x – 1)
= 63(x – 1)
10.
2x 2x 1
π π+ −
=
Set B
1. 6x
= 611
2. 95y
= 915
3. 126z
= 123
4. 10a – 4
= 10-9
5. 72b + 2
= 7b – 3
6. 23n – 7
= 2n + 5
7. 34(x + 2)
= 35x – 2
8. 8– (3 – 2x)
= 83(-4 + x)
9. 12
44
2
=−xx
10.
24x 4x
5 5−
=
Set C
1. 42x
= 49
2. 38y
= 312
3. 611z + 2
= 63z – 10
4. 24y + (2 – y)
= 23 – 5y
5. x 5
8 8=
6. x 3 2
5 5+
=
7.
2x 2x 1
7 7 −
=
8.
2x x 6
9 9 +
=
9.
22x x 3
π π−
=

4
10. ( ) ( )
22x 5x 3
2 2
+
=
Lesson 2
Review of the Laws of Exponents
Let us review the Laws of Exponents for easy reference.
For any real numbers a and b, and any positive real numbers m and n,
a. am
an
= am + n
b. (am
)n
= amn
c. (ab)n
= an
bn
d.
m
m n
n
a
a ,a 0
a
−
= ≠
e.
n n
n
a a
,b 0
b b
  = ≠ 
 
f. a0
= 1
Examples:
Simplify each expression. Express answers with positive exponents:
1. (x3
)(x6
)
(x3
)(x6
) = x3 + 6
= x9
2. (x -3
)2
(x -3
)2
= x(-3)(2)
= x-6
= 6
1
x
3. (2x -5
)-3
(2x -5
)-3
= 2-3
x15

5
Express rational exponents
in radical form and simplify.
=
15
3
x
2
=
15
x
8
4.
5
7
16x
12x
5
7
16x
12x
=
5
7
16 x
12 x
⋅
= 5 74
x
3
−
⋅ Simplify
= 24
x
3
−
⋅
= 2
4 1
3 x
⋅
= 2
4
3x
5.
3
2
3
2
3
1
125
64










−
x
x
3
2
3
2
3
1
125
64










−
x
x
=
3
2
125
64






·
3
2
3
2
3
1










−
x
x
=
2
3
125
64






·
3
2
3
2
3
1







 +
x
=
2
5
4






·
3
2
3
3








x
= 





25
16
· [ ]3
2
1
x

6
=
25
16 3
2
x
Try this out
Simplify each expression. Express answers with positive exponents:
Set A
1. (x6
)(x7
)
2. (3x4
)(-6x7
)
3. (x5
)4
4. (3x3
)2
5.
9
5
8x
2x
6.
2
5
15x
25x
−
−
7.
6
4
21x
14x−
−
8.
( )
( )
25
32
2x
4x
−
−
9.
29
5
8x
2x
−
 
 
 
10.
( )
( )
132
23
2x
3x
−
−−
 −
 
 
  
Set B
1. (5x-4
)(-x2
)
2. (-2x-3
)(-4x-2
)
3. (3x-4
)3
4. (-5x-4
)2
5.
8
3
12x
20x

7
6.
6
2
33x
24x
−
−
7.
9
13
48x
80x−
−
8.
( )
( )
24
32
2x
3x
−
−
−
9.
25
9
6x
8x
−
 
− 
 
10.
( )
( )
212
32
4x
2x
−−
−−
 
 
 −  
Set C
1.
6
4
27x
21x
−
2.
2 3
9
(2x )
8x
3.
2 4
3 2
(3x )
(9x )
−
−
4.
6 2
3 4
(8x )
(2x )
5.
2
1 3
2
8x
27x
 
 
 
 
6.
1
6 2
2
64x
36x
−
 
 
 
7.
29
13
32x
72x
−
−
 
− 
− 
8.
( )
( )
233
22
2x
3x
−
 
 
 −  

8
9.
22
4
2x
8x
−−
  −  
  
10.
( )
( )
322
32
2x
2x
−−
−−
 −
 
 −  
Lesson 3
Finding the Roots of Exponential Equation
The Property of Equality for Exponential Equation which is also known as
Equating-Exponents Property implies that in an exponential equation, if the
bases are equal, the exponents must also be equal.
Examples:
Solve each exponential equation.
1. 24x + 2
= 8x – 2
Use laws of exponents to make the bases equal. Then apply the Equating
Exponents Property.
24x + 2
= 8x – 2
24x + 2
= 23(x – 2)
4x + 2 = 3(x – 2)
4x + 2 = 3x – 6
x = -8
2. 9-x
=
1
27
Exponents Property.
9-x
=
1
27
32(-x)
= 27-1

9
3-2x
= (33
)-1
3-2x
= 3-3
-2x = -3
x =
3
2
−
−
x =
3
2
3.
2x 5x 1
2
16
−
=
Exponents Property.
2x 5x 1
2
16
−
=
2x 5x 1
2 16− −
=
( )
12x 5x 4
2 2
−−
=
2x 5x 4
2 2− −
=
x2
– 5x = -4
x2
– 5x + 4 = 0
(x – 1)(x – 4) = 0
x = 1 or x = 4
Try this out
Solve for x in each exponential equation.
Set A
1. 2x
= 128
2. 5x
= 125
3. 2x
=
1
2
4. 92x
= 27
5. 2x – 1
= 32
6. 1000x
= 1002x – 5

10
7. 43x + 1
= 8x – 1
8. 93x
= 27x – 2
9. 8x – 1
= 163x
10.93x + 1
= 273x + 1
Set B
1. 9x
= 27
2. 4x
= 128
3. 4x
=
1
2
4. 3x + 2
= 27
5. 25x + 1
= 125x
6. 4x
= 0.0625
7. 3– x
=
243
1
8. 8x + 3
=
1
16
9.
x
2x 11
27
3
−
+  = 
 
10.
3 2x
x1
8
4
−
−  = 
 
Set C
1.
x
1
4
2
  = 
 
2. x 1
4
8
=
3. 5x + 3
= 25
4. 9x
= 27x + 1
5. 73x + 2
= 49x
6. 1213x
= 11x – 1
7.
x 3
5 x3
3 81
+
+
=
8.
2x x
16
1
25
+
  = 
 

11
9. ( ) 3
2
5
−x
= 0.04
10.
2
1
8
1 3
1
=





x
Lesson 4
Determining the Zeros of Exponential Functions
As in other function, the zero of an exponential function refers to the value
of the independent variable x that makes the function 0. Graphically, it is the
abscissa of the point of intersection of the graph of the exponential function and
the x-axis.
To find the zero of an exponential function f(x), equate f(x) to 0 and solve
for x.
Examples:
Determine the zero of the given exponential function.
1. f(x) = 2x
To find the zero of the function, equate it to 0 and solve for x.
f(x) = 2x
= 0
2x
= 0
The resulting equation suggests that f(x) has no zero since no real
value of x will make 2x
= 0 a true statement.
2. g(x) = 34x – 8
– 1
g(x) = 34x – 8
– 1 = 0
34x – 8
– 1 = 0
34x – 8
= 1
34x – 8
= 30
4x – 8 = 0
4x = 8

12
x = 2
The zero of g(x) is 2.
3. h(x) =
2x 3
1
9
3
+
  + 
 
h(x) =
2x 3
1
9
3
+
  − 
 
= 0
2x 3
1
9
3
+
  − 
 
= 0
2x 3
1
3
+
 
 
 
= 9
2x 3
1
3
+
 
 
 
= 32
( )
2x 31
3
+−
= 32
( )
2x 3
3
− −
= 32
-2x – 3 = 2
-2x = 5
x =
5
2
−
The zero of h(x) is
5
2
− .
4. y = 22x + 3
–
x 1
1
512
−
 
 
 
y = 22x + 3
–
x 1
1
512
−
 
 
 
= 0
22x + 3
–
x 1
1
512
−
 
 
 
= 0

13
22x + 3
=
x 1
1
512
−
 
 
 
22x + 3
= ( )
x 11
512
−−
22x + 3
= ( )
x 119
2
−−
 
  
22x + 3
= ( )
x 19
2
−−
22x + 3
= ( )
9x 9
2
− +
2x + 3 = -9x + 9
11x = 6
x =
6
11
The zero of y is
6
11
.
Try this out
Determine the zeros of the given polynomial function.
Set A
1. f(x) = 3x
2. g(x) = 3x + 2
- 27
3. h(x) = 4x – 1
– 64
4. p(x) = (7-x
)2
– 343
5. F(x) = (0.2)x – 2
– 54x
6. G(x)= 82x
– 22x + 1
7. H(x) =
x 3
1 x1
8
2
−
−  − 
 
8. P(x) = 4x(x – 5)
–
3
1
16
 
 
 
9. y = ( )
x 3
3x 1
27 3
−
−
−

14
10.y =
4x 3
2 16
3 81
+
  − 
 
Set B
1. f(x) = 22x – 1
2. g(x) = 165 + x
– 4
3. h(x) = 103x
– (0.001)x + 3
4. p(x) = 2x(x – 3)
–
1
16
5. F(x) =
3x 4
3 2x1
2
64
−
−  − 
 
6. G(x) = 343 – 492x – 1
7. H(x) = ( )
x 2
3x 1 1
125
5
−
−
 −  
 
8. P(x) =
x 3
2 32
3 243
−
  − 
 
9. y =
2x 1
3 27
5 125
+
  − 
 
10.y =
3x 1 x
4 49
7 16
−
   −   
   
Set C
1. f(x) = 92x + 2
– 27
2. g(x) = 1253x + 7
–
x 3
1
5
−
 
 
 
3. h(x) = 25x + 1
– 82x – 3
4. p(x) = 275x – 6
– 97x + 3
5. F(x) =
x
4 1
81
27
−
6. G(x) = (9x
)(3x
) – 243
7. H(x) =
x 5
3 729
2 64
+
  − 
 

15
8. P(x) =
2x 3
4 27
3 64
−
  − 
 
9. y =
3x 1
2 625
5 16
+
  − 
 
10.y =
9
4
2
3
3
−





−x
Let’s summarize
1. An exponential equation is an equation where the variable is the
exponent.
2. In solving exponential equations, the Property of Equality for Exponential
Equation is used. Stated as follows: “If a, b, and c are real numbers and
a ≠ 0, then, ab
= ac
if and only if b = c.”
3. For any real numbers a and b, and any positive real numbers m and n,
a. am
an
= am + n
b. (am
)n
= amn
c. (ab)n
= an
bn
d.
m
m n
n
a
a ,a 0
a
−
= ≠
e.
n n
n
a a
,b 0
b b
  = ≠ 
 
f. a0
= 1
4. The Property of Equality for Exponential Equation which is also known as
Equating-Exponents Property implies that in an exponential equation, if
the bases are equal, the exponents must also be equal.
5. The zero of an exponential function refers to the value of the independent
variable x that makes the function 0.
6. Graphically, the zero of an exponential function is the abscissa of the point
of intersection of the graph of the exponential function and the x-axis.

16
7. To find the zero of an exponential function f(x), equate f(x) to 0 and solve
for x.
What have you learned
1. If 22x + 1
= 25
, what is x?
2. Find x if 4x + 1
= 2.
3. Simplify the expression (5x4
)3
.
4. Express
23
7
9x
36x
−−
 
 
− 
without negative exponent.
5. Solve for x in the equation 9(42x + 1
) = 36x
6. What are the values of x in
2x 2x 1
4 8 −
= ?
7. Determine the zeros of the exponential function F(x) = 5x – 2
.
8. Find all the zeros of f(x) = 7x – 3
– 49.
9. Where will the graph of g(x) =
x
1
4
 
 
 
–
2x 1
1
2
+
 
 
 
cross the x-axis?
10.What value of x will make h(x) = 322x
–
2x
1
16
−
 
 
 
equal to 0?

17
Answer Key
How much do you know
1. 4
2. 3
3. 16x10
4. 10
4
x
5. 2
6. 2 ± 2
7. no zero
8. 5
9. 0 and
2
3
10. 0
Try this out
Lesson 1
Set A
1. 9
2. 4
3.
5
3
4. 9
5. -3
6. 1
7. -3
8. -3
9.
5
1
10. -1

18
Set B
1. 11
2. 3
3.
2
1
4. -5
5. -5
6. 6
7. 10
8. 9
9. 4 and -3
10.
2
22 ±
Set C
1.
2
9
2.
2
3
3. -
2
3
4.
8
1
5. 25
6. 1
7. 1
8. 3 and -2
9.
2
3
and -1
10.
2
1
and -3

19
Lesson 2
Set A
1. x13
2. -18x11
3. x20
4. 9x6
5. 4x4
6. 7
5
3
x
−
7.
2
3 10
x
−
8.
4
4
x
−
9. 8
16
1
x
10.
72
1
−
Set B
1. 2
5
x
−
2.
x
8
3. 12
27
x
4. 8
25
x
5.
5
3 5
x
6. 8
8
11
x
−
7.
5
3 22
x
−

20
8. 2
108
x
9.
9
16 8
x
10.
4
16
x
Set C
1.
7
9 2
x
−
2. 3
1
x
3. 2
6561
x
4. 4
5. 3
1
9
4
x
6. 4
3
4
x
7. - 31
16
81
x
8. 26
5184
1
x
9. 12
4
1
x
10. -
8
20
x

21
Lesson 3
Set A
1. 7
2. 3
3. -1
4.
4
3
5. 6
6. 10
7. -
5
1
8. -2
9. -
3
1
10. -
3
1
Set B
1.
2
3
2.
2
7
3. -
2
1
4. 1
5. 2
6. -2
7. 5
8. -
3
13
9. -
5
3

22
10.
7
6
Set C
1. -2
2. -
2
3
3. -1
4. -3
5. -2
6. -
5
1
7. -
11
57
8. 0 and -1
9. 3
10.-1
Lesson 4
Set A
1. No rational zero
2. 1
3. 4
4. -
2
3
5.
5
2
6.
4
1
7. 0
8. 2 and 3
9. -
3
7

23
10.
4
1
Set B
1. No rational zero
2. -
2
9
3. -
2
3
4.
2
73 i±
5. -
16
27
6.
8
7
7.
11
7
8. 8
9. 1
10.
5
1
Set C
1. -
4
1
2. -
5
9
3. 10
4. 24
5. -3
6.
3
5
7. 1
8. 0

24
9. -
3
5
10. 1
How much have you learned
1. 2
2. -
2
1
3. 125x12
4. 16x20
5. -1
6.
2
33 ±
7. none
8. 5
9. It will not cross the x-axis
10.0

Module 2 exponential functions

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Module 2 exponential functions