WRITING AND GRAPHING LINEAR EQUATIONS 1.ppt

Equation of a Line
Equation of a Line
TWO-POINT FORM
TWO-POINT FORM

Write the equation of a line in slope-intercept
form that passes through points (3, -4) and
(-1, 4).
1) Find the
slope.
4 – (-4) 8
-1 – 3 -4
m = -2
2) Choose either point and
substitute. Solve for b.
y = mx + b (3, -4)
-4 = (-2)(3) + b
-4 = -6 + b
2 = b
Substitute m and b in equation.
Y = mx + b
Y = -2x + 2
Do you
remember
the slope
formula?

Write the equation of the line in
slope-intercept form that passes through
each pair of points.
1) (-1, -6) and (2, 6)
2) (0, 5) and (3, 1)
3) (3, 5) and (6, 6)
4) (0, -7) and (4, 25)
5) (-1, 1) and (3, -3)

Equation of Line
Equation of Line
POINT-SLOPE FORM
POINT-SLOPE FORM

Point-Slope Form
and Writing
Equations
• Suppose you know that a
line passes through the
point (3, 4) with slope 2.
You can quickly write an
equation of the line using
the x- and y-coordinates
of the point and using
the slope.
• The point-slope form of
the equation of a
nonvertical line that
passes through the
(x1, y1) with slope m.
y – y1 = m(x – x1)
(if you know a point and the
slope, use this form)

Let’s try a couple.
Using point-slope form, write the equation of a line
that passes through (4, 1) with slope -2.
y – y1 = m(x – x1)
y – 1 = -2(x – 4)Substitute 4 for x1, 1 for y1 and -2 for m.
Write in slope-intercept form.
y – 1 = -2x + 8 Add 1 to both sides
y = -2x + 9

One last example
Using point-slope form, write the equation of a line
that passes through (-1, 3) with slope 7.
y – y1 = m(x – x1)
y – 3 = 7[x – (-1)]
y – 3 = 7(x + 1)
Write in slope-intercept form
y – 3 = 7x + 7
y = 7x + 10

If you know two points on a line, first use
them to find the slope. Then you can write an
equation using either point.
• Step one – Find the
slope of a line with
points (-4, 3), (-2, 1)
 
1
2
2
4
2
3
1
1
2
1
2











m
x
x
y
y

Step Two – Use either point to write the
equation in point-slope form. Use (-4, 3)
y – y1 = m(x – x1)
Y – 3 = -1[x – (-4)]
Y – 3 = -1(x + 4)
Write in slope-intercept form
Y – 3 = -1(x + 4)
Y – 3 = -x - 4
Y = -x - 1

Practice with Equations of Lines
Answer the following questions dealing with equations
and graphs of straight lines.
1) Which of the following equations passes
through the points (2, 1) and (5, -2)?
a. y = 3/7x + 5 b. y = -x + 3
c. y = -x + 2 d. y = -1/3x + 3

2) Does the graph of the straight line
with slope of 2 and y-intercept of 3
pass through the point (5, 13)?
Yes
No

3) The slope of this line is 3/2?
True
False

4) What is the slope of the line
3x + 2y = 12?
a) 3
b) 3/2
c) -3/2
d) 2

5) Which is the slope of the line
through (-2, 3) and (4, -5)?
a) -4/3
b) -3/4
c) 4/3
d) -1/3

6) What is the slope of the line shown in the
chart below?
X 1 3 5 7
Y 2 5 8 11
a) 1
b) 3/2
c) 3
d) 3/5

7) Does the line 2y + x = 7 pass through
the point (1, 3)?
True
False

8) Which is the equation of a line
whose slope is undefined?
a) x = -5
b) y = 7
c) x = y
d) x + y = 0

9) Which is the equation of a line that
passes through (2, 5) and has slope -3?
a) y = -3x – 3
b) y = -3x + 17
c) y = -3x + 11
d) y = -3x + 5

10) Which of these equations
represents a line parallel to the line
2x + y = 6?
a) Y = 2x + 3
b) Y – 2x = 4
c) 2x – y = 8
d) Y = -2x + 1

WRITING AND GRAPHING LINEAR EQUATIONS 1.ppt

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WRITING AND GRAPHING LINEAR EQUATIONS 1.ppt