Download 5.1 Writing Equations in Slope

Algebra
5.1
Writing Linear Equations in
Slope Intercept Form
Slope Intercept Form
Write an equation of the line whose slope m is
-2 and whose y-intercept b is 5.
m = -2
b=5
y = mx + b
y = -2x + 5
b=5
y-intercept (0,5)
Rise -2
m = -2
Run
1
Graph of y = -2x + 5
Writing an Equation of a Line
from a Graph
STEPS
By looking at the graph:
1. Identify the y-intercept b
2. Find another point on the “corner” of a
grid box (coordinates are whole
numbers)
3. Either count rise and run from b to the
other point, or use the slope formula to
find m.
4. Plug in m and b to the equation
y = mx + b.
Example (from graph to equation)
b = -2
Using visual count:
m = Rise 1
Run 3
Rise 1
•
•
Run 3
(3,-1)
(0,-2)
Equation:
1
y  x2
3
=
1
3
Using slope formula:
m = -1 –(-2)
3-0
= 1
3
Write the equation
b3
3
m
2
3
y x3
2
b  1
1
m
4
1
y  x 1
4
Write the linear equation
A plumber charges $66 for the first hour of a service
call and $45 for any additional hours. Write a linear
model to reflect the plumber’s charges and use the
equation to determine the cost of a 3-hour service call.
Let C represent the cost of the service and h
represent the number of hours.
C = 45h + 66
C = 45(2) + 66
C = 90 + 66
C = 156
Turn to page 275
Let’s go through Example 4 together
Homework
pg. 276 #12-36, 38-40