1. 2-4: Writing Linear Equations Using Slope Intercept Form

2. Writing Linear Equations
To write a linear equations, there are two things that you will need.
Slope and Y- intercept
We will substitute this information into the following equation.

3. Slope-Intercept Form
y = mx + b [or f(x) = mx + b]
m is the slope
b is the y-intercept

4. Find the equation of the line from a graph
What is the
y-intercept?
b = -2
What is m?
m =
y = x -2 x y

5. Find the Equation of the Line
b = ?
b = 1
m = ?
m = -
y = - x + 1 x y

6. Find the Equation of the Line
b = ?
b = 4
m = ?
m = 0
y = 0x+4
y=4 x y

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

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

9. 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 = mx + b
1 = -1(2) + b
1 = -2 + b
3 = b

10. continue
Using the information just found, substitute it into the slope intercept formula.
y = mx + b
y = (-1)x + (3)

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

12. Find the Equation Given a Point and a slope
Another method that can be used to generate an equation of a line from a point and a slope is the point-slope formula.
y – y1 = m(x – x1)

13. Find the Equation Given Two Points
Given m = -5 and the point (7,1).Write an equation of a line using the point-slope formula.
y – 1 = -5(x – 7)
y – 1 = -5x + 35
y = -5x + 36