5-4 Notes: Writing a Function Rule

Example 1: Writing a Function Rule from a Table What do you do to x to get f(x)? X f(X) 1 5 2 6 3 7 4 8 Relate: f(x) equals x plus 4 f(x)= x + 4

2. x y 1 3 9 6 36 81 Relate: y equals x times itself y = x2

3. x f(x) 1 -1 2 3 4 Relate: f(x) equals x minus 2 f(x)= x-2

4. x y 1 2 4 3 6 8 Relate: y equals x times 2 y = 2x

5. x y 1 3 2 4 5 6 Relate: y equals x plus 2 y = x + 2

Example 2: Real World Problem Solving A carpenter buys finishing nails by the pound. Each pound of nails costs $1.19. Write a function rule to describe this relationship. Relate: cost equals 1.19 times nails (x) C(x) = 1.19x

C(12)=1.19 (12) $14.28 How much do 12lb of finishing nails cost? 2. From problem 1. c(x)= 1.19x: How much do 12lb of finishing nails cost? C(12)=1.19 (12) $14.28

Relate: profit is $18 times lawns mowed minus cost of mower. 3. Suppose you borrow money from a relative to buy a lawn mower that costs $245. You charge $18 to mow a lawn. Write a rule to describe your profit as a function of the number of lawns mowed. Relate: profit is $18 times lawns mowed minus cost of mower. Define: let n=number of lawns mowed & p=profit p(n)=18n-245

Define: let h=number of hours & p=total profit p(h)=15h-199 4. Suppose you buy a word-processing software package that costs $199. You charge $15 per hour for word processing. Write a function rule to describe your profit as a function of the number of hours you work. Relate: total profit is $15 times number of hour of word processing minus cost of word processor. Define: let h=number of hours & p=total profit p(h)=15h-199

HW # 14 Page 256 (1-18)