Download Section 9.1

Algebra 2B
Day 10
9.1 Inverse and Joint Variation
 Daily Openers
 Go over and collect homework
9.1 Inverse and Joint Variation
direct variation –
inverse variation –
y
k

y  kx or
x
k  y
yx = k or
x
Show the graphs of each and how they relate:
Direct
Indirect
 = 52X
 = 1x
 = 34X
 = 5 3x
 = 7x
=6
Ex. The area, A (in square centimeters), of a rectangle varies directly with its width, w (in centimeters).
When the width is 5 centimeters, the area is 15 square centimeters. Write an equation that relates A and w.
Ex. The time, t (in minutes), you need to type a 2000-word paper varies inversely with the rate, r (in words
per minute), that you can type. When typing 40 words per minute, you can finish in 50 minutes.
Joint variation – a quantity varies directly as the product of two or more other quantities:
z= kxy
Ex. Find an equation that relates the variables (joint variation)
X = 3,
Y = 6,
Z=9
Ex. Page 492 # 36, 52
Homework – pages
Daily Openers – 1. Factor: (a) 4 x 2  17 x  15
(b) 9 y 2  25
2. Solve: 3 x 2  18 x  24
3. Solve: 9 x 2  6 x  0
4. Solve: ln 4 + ln x = 5
5. page 486 #2, 6