# 2.4 Write Equations Of Lines Examples And Worksheet - Chapter 2, Linear Equations And Functions

2.4
Write Equations of Lines
Before
You graphed linear equations.
Now
You will write linear equations.
Why?
So you can model a steady increase or decrease, as in Ex. 51.
Key Vocabulary
KEY CONCEPT
point-slope form
Writing an Equation of a Line
Given slope m and y-intercept b
Use slope-intercept form:
y 5 mx 1 b
Given slope m and a point (x
, y
)
Use point-slope form:
1
1
y 2 y
5 m(x 2 x
)
1
1
Given points (x
, y
) and (x
, y
)
First use the slope formula to find m.
1
1
2
2
Then use point-slope form with either
given point.
E
1
Write an equation given the slope and y-intercept
X A M P L E
Write an equation of the line shown.
y
2
4
Solution
3
From the graph, you can see that the slope is m 5
}
3
x
1
4
and the y-intercept is b 5 22. Use slope-intercept
(0, 22)
form to write an equation of the line.
y 5 mx 1
b
Use slope-intercept form.
3
3
y 5
x 1 (22)
Substitute
for m and
2
2 for b.
}
}
4
4
3
y 5
x 2 2
Simplify.
}
4
at
G
P
for Example 1
UIDED
RACTICE
Write an equation of the line that has the given slope and y-intercept.
3
7
1.
m 5 3, b 5 1
2.
m 5 22, b 5 24
3.
m 5 2
, b 5
}
}
4
2
98
Chapter 2 Linear Equations and Functions