Daily Starter:
1. Write down a real-life example where one
variable increases as a second variable
increases.
2. Write down a real-life example where one
variable increases as a second variable
decreases.
Feb 16­1:20 PM
1
Section 11.3
Direct and
Inverse
Variation
2
Direct Variation:
The variable y increases as the
variable x increases.
y = kx
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3
direct variation
y = kx
x = 2
y = 4 x = 45
y = 81 Jan 27­7:37 PM
4
y = kx
Example:
Write the equation that relates x
and y if x=2 and y=4 when x and y
vary directly.
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5
y = kx
Example:
Write the equation that relates x
and y if x=45 and y=81 when x and y
vary directly.
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6
Inverse Variation:
The variable y decreases as the
variable x increases.
xy = k
y=
k
x
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7
direct variation
y = kx
x = 2
y = 4 y = 2x
x = 45
y = 81 y = 9/5 x
indirect variation
y = k/x Jan 27­7:37 PM
8
y=
Example:
k
x
Write the equation that relates x
and y if x=2 and y=4 when x and y
vary inversely
Feb 16­1:20 PM
9
y=
Example:
k
x
Write the equation that relates x
and y if x=45 and y=81 when x and y
vary inversely.
Feb 16­1:20 PM
10
Do the equations model direct
variation, inverse variation, or
neither?
x=
(What is the constant of variation?)
4
y
y = 7x - 2
a = 12b
ab = 9
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11
Homework:
Section 11.3
p. 659
#12 - 32 even
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12
Mar 1­8:04 AM
13
Mar 1­8:05 AM
14
Mar 1­8:06 AM
15
Homework:
Worksheet
Feb 22­5:37 PM
16