1. 5-4 Writing a Function Rule

2. Ex. 1 Writing from a Table Ask “How do I get from x to f(x)?”
Add 4 to x each time
f(x) = x + 4
How do I get from x to y
x times itself
y = x2 x
f(x) 1 5 2 6 3 7 4 8 x y 1 3 9 6 36 81

3. Your Practice Write Function Rule multiply x by 2 y = 2x
Add 2 to x
y = x + 2 x y 1 2 4 3 6 8 x y 1 3 2 4 5 6

4. Ex. 2/3 Story Problems
The exhibit at the left is a scale model of a desk top computer. It is about 20 times the size of a normal sized desk top computer.
A. Write a function rule
B. Find length of space bar if 5 inches on regular computer.
A. Larger is 20 times normal
L = 20n
B. Use function rule
L = 20(5)
L = 100 inches

5. Story Problems Cont.
Suppose you buy a word-processing software package for $199. You charge $15 per hour for word processing. Write a rule to describe your profit as a function of the number of hours you work.
Describe how to find the profit
Profit is 15 dollars per hour – cost of software package.
P = 15d – 199

6. Your Practice
A carpenter buys finishing nails by the pound. Each pound of nails costs $ Write a function rule to describe this relationship. How much do 12 lbs of finishing nails cost?
Function Rule
Total cost is price per pound times number of pounds
c = 1.19p
Cost of 12 lbs
c = 1.19(12)
c = $14.28