2.3.notebook
September 20, 2011
KnowDirect Variation
Constant of Variation
How to find missing elements of the direct variation
equation.
Section 2.3: Identifying Direct Variations
from tables and equations.
Making real world connections
Direct Variation: Constant of Variation:
Understand how to use direct variation equation to find
needed information in an applied situation. Understand how
the parts of the dv equation relate to one another.
Do- Be able to write and interpret a direct variation.
Be able to identify direct variation from a table.
Be able to identify direct variation from an equation.
Be able to apply concepts learned about direct variation
to solve real world problems!
Sep 15­11:04 AM
Sep 16­10:35 AM
From a Table
Direct Variation From an Equation
If it is a direct variation, what is the variation constant?
A. x y
2 8
3 12
5 20
B.
x y
1 4
2 7
5 16
C.
x y
­6 ­2
3 1
12 4
D. x y
­1 ­2
3 4
6 7
E.
x y
­9 5
a. 4y = 2x
b. y = ­3x ­ 3
c. 5x ­ 2y = 0
d. 3y + 7 = ­5x
3 ­123
6 358
If it is a direct variation, what is the variation constant?
Sep 16­10:42 AM
For each variation, find the variation constant. Then
find the value of y when x = -3
a. y = 4 and x = ­2
Sep 17­10:04 AM
Sep 16­11:00 AM
For each variation, find the variation constant. Then
find the value of y when x = -3
b. y = 3 and x = 7
c. y = 3 and x = 2
5 5
Sep 17­10:30 AM
1
2.3.notebook
September 20, 2011
Section 3: Direct Variation
For the function, y varies directly with x. Find the constant of
variation.
x
2
4
5
y
-6
-12
-15
Homework
Suppose y varies directly with x. If y = 7 when x = 2, find y
when x = 3.
The number of minutes a freight train takes to pass an
intersection varies directly with the number of cars in the
train. A 150-car train passes in 3 minutes. How long will a
280-car train take to pass? Write your answer in minutes and
seconds.
Sep 16­8:16 AM
Pg.74-76: 1-27 odds, 52
Sep 16­8:39 AM
2