1. Writing Function Rules
Teacher Twins©2014

2. Warm Up
Graph each function.
1. y = 4x y = -3x + 1

3. Writing Functions
Rules

4. Ex 1: Write a function rule for the given table of values.
Think how does -1 become -2?
Multiply by 2 or add -1. Try both to see which one works.
-1 x 2 = = -2
0 x 2 = = -1
1 x 2 = 2 Does not
2 x 2 = 4 work.
works
Function Rule y = 2x

5. Ex 2: Write a function rule for the given table of values.
How does -2 become -10? Guess and check functions until you find the correct one.
X 5 does not work
+ -8 does not work
Try multiplying then adding a number or subtracting a number.
X3 – 4
-2(3) – 4 = -10
0(3) – 4 = -4
2(3) – 4 = 2
4(3) – 4 = 8
Works
y = 3x - 4

6. Practice
Write the function rule.
y = - 3x
y = x + 6

7. Closure
How many rules can you create that make
-2 turn into -6?