2.4 writing linear equations

2-4: Writing Linear Equations

Today’s objectives:
1. I will write linear equations in
slope-intercept form.
2. I will determine the slope and y-
intercept of a linear equation.
3. I will write linear equations of
parallel and perpendicular lines.

Slope-Intercept Form

• y = mx + b
[or f(x) = mx + b]
• m is the slope
• b is the y-intercept

Find the Equation of the Line

• What is the
y-intercept?
• b = -2 x

• What is m?
3
• m= 2
3
• y = 2 x -2 y


•b=?
•b=1
x
•m=?
•m= - 1
2
1
•y= x+1
-
2 y

• b=?
• b=4
• m=? x
• m=0
• y = 0x+4
• y=4
y

Find the Slope and y-intercept of
each Equation:
3
1) y = -4x + 3 3) 8x + y = 4
m = -4 m = -8
3
b=3 b=4
1
2) y = 5 - 2 x 4) 4x - 2y = 10
1
m= 2 - m=2
b=5 b = -5

Find the Equation Given the
Slope and y-intercept
1) m = -3, b = 1
y = -3x + 1
2
2) m = - b = -4
5
,
2
y=-5x-4

Find the Equation Given the
Slope and a Point
Given m = -1, (2, 1)
First, calculate b by substituting the slope and
the coordinates into y = mx + b.
y = -1x + b
1 = -1(2) + b
1 = -2 + b
3=b
y = -1x + 3

Find the Equation Given
Two Points
Given (-1, 3) and (2, 1)
First, calculate the slope:
(1 − 3) −2
m= =
(2 − −1) 3
Second, find b. Use either point...
m = − 2 , (2, 1)
3
2
1= − (2) +b
3
4
1 − +b
= 3
2 7
7
=b y =− x +
3 3 3

2.4 writing linear equations

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2.4 writing linear equations