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• What is m?• m = • y = x -2

x

y

3

23

2

Find the Equation of the Line

• b = ?• b = 1• m = ?• m = -

• y = - x + 1

x

y

1

21

2

Find the Equation of the Line

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

x

y

Find the Slope and y-intercept of each Equation:1) y = -4x + 3

m = -4

b = 3

2) y = 5 - x

m = -

b = 5

3) 8x + y =

m = -8

b =

4) 4x - 2y = 10

m = 2

b = -5

1

21

2

3

4

3

4

Find the Equation Given the Slope and y-intercept

1) m = -3, b = 1

y = -3x + 1

2) m = - , b = -4

y = - x - 4

2

52

5

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 GivenTwo PointsGiven (-1, 3) and (2, 1)

First, calculate the slope:

Second, find b. Use either point...m = , (2, 1)

1 = (2) + b

1 = + b

= b

( )

( )m

1 3 2

2 1 3

2

3

2

3

4

3

7

3y x

2 7

3 3