1. 3 hr 5 hr 8 hr Hours worked Charge
A plumber charged $110 for a three hour job and $160 for a five hour job. At this rate, how much would he charge for an eight hour job. 
plumbers normally charge a basic fee to just show up, and then they charge per hr.
Hours worked
Charge
3 hr
$110
5 hr
$160
8 hr $?

2. 240
$235
220
200
180
160
140
120
100 80
Distance 60 40 20 1 2 3 4 5 6 7 8 9 10 11 12
Time

3. Lesson 3.8 Linear Functions f(2) = 5 ( 2, 5) Function notation
A linear function is a linear equation written with f(x) instead of y
Function notation
Equation notation
Input, output
Ordered Pair
f(2) = 5
( 2, 5)

4. f(x) = x + 4 Example: Find an equation of the linear function f
a) m = , b = 4
f(x) = mx + b
f(x) = x + 4

5. f(-2) = 1 , m = 3
b) 
step1: Rewrite the function notation as ordered pair x1 y1
f(-2) = 1
 (-2, 1)
step2: write the equation using the point slope form
y – y1 = m(x – x1)
y – 1 = 3(x + 2)
y – 1 = 3x + 6
y = 3x + 7
step3: write the equation in the function notation.
f(x) = 3x + 7

6. f(0) = 7 ,  f(4) = -1
c) 
step1: rewrite the function notation as ordered pair
f(0) = 7
f(4) = -1
 (0, 7)
 (4, -1) x1 y1 x2 y2
step2: find the slope
(0, 7) and (4, -1)
step3: write the equation using the point slope form
y – y1 = m(x – x1)
y – 7 = -2(x – 0)
y – 7 = -2x
y = -2x + 7
step4: write the equation in the function notation.
f(x) = -2x + 7

7. f is a linear function f(x) = -x + 4 d)
If f(1) = 3 ,  f(-1) = 5, find f(10)=? and f(100)=?
step1: rewrite the function notation as ordered pair
f(1) = 3
 (1, 3)
f(-1) = 5
 (-1, 5) x1 y1 x2 y2
step2: find the slope
(1, 3) and (-1, 5)
step3: write the equation using the point slope form
step5: find f(10) and f(100)
y – y1 = m(x – x1)
f(10) = - (10) + 4
y – 3 = -1(x – 1)
= -6
y – 3 = -x + 1
y = -x + 4
f(100) = -(100) + 4
step4: write the equation in the function notation.
= -96
f(x) = -x + 4

8. Home Work
(2 – 22 + even 28, 29, 30)
Page 149, 150