1. Academy Algebra II 8.1: Model Inverse & Joint Variation
HW: p.555 (4 – 26 even)
Quiz : Tuesday, 2/10
This Thursday: go to room 303

2. Two variables show inverse variation if they are related as follows:
y varies inversely with x

3. Two variables show direct variation if they are related as follows:
y varies directly with x

4. z varies jointly with x and y
Joint variation occurs when a quantity varies directly with the product of two or more other quantities.
z varies jointly with x and y

5. Tell whether x and y show direct variation, inverse variation, or neither.

6. Tell whether x and y show direct variation, inverse variation, or neither.

7. The variables x and y vary inversely
The variables x and y vary inversely. Use the given values to write an equation relating x and y. Then find y when x = 3.
1.) x = 1, y = 9
2.) x = 7, y = 2

8. Write an equation relating x, y , and z given that z varies jointly with x and y. Then find z when x = -4 and y = 5.
1.) x = 8, y = 6, z = 12
2.) x = 6, y = -7, z = -3

9. Determine whether x and y show direct variation, inverse variation, or neither.
1.) ) X Y 12
132 18
198 23
253 29
319 34
374 X Y 4 21 6 14 8
10.5
8.4 10 12 7

10. Problem Solving: p.556 #37
The number n of photos your digital camera can store varies inversely with the average size s (in megapixels) of the photos. Your digital camera can store 54 photos when the average photo size is 1.92 megapixels. Write a model that gives n as a function of s. How many photos can your camera store when the average photo size is 3.87 megapixels?