1. 5-4 Review Notes: Writing a Function Rule 5-5 Review: Direct Variation

2. 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

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

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

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

6. 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

7. Direct Variation A function in the form y = kx.
The constant of variation (k) is the coefficient of x.
Step 1: Solve for y.
Step 2: Is it in y = kx form?

8. Ex 1: Is the equation in direct variation form?
5x + 2y = 0
5x + 2y = 9
7y = 2x
y – 7.5x = 0

9. Ex. 2: Writing an equation given a point .
(4, -3)
(-3, -6)
(-3, 2)

10. Ex. 3: Does the table vary directly, if so write an equation in direct variation form.-3
2.25 1
-0.75 4 6
-4.5

11. X Y 2 -1 4 1 6 3 9
4.5

12. HW #12
Pg. 256 (1-17)
Pg. 264 (1-21 odd)