1. Lesson 3­4.notebook November 05, 2012
Lesson 3.4:
*direct variation ­ an equation in the form, y = kx, where k = 0
*constant of variation or constant of proportionality ­ the "k" in an
equation in the form, y = kx
***Same thing as the slope....
however, direct variation equations will always
go through the origin!
1

2. Lesson 3­4.notebook November 05, 2012
Lesson 3.4 examples:
Graph each equation. Y
A) y = ­4x
X
constant of variation =
slope =
2

3. Lesson 3­4.notebook November 05, 2012
B) y = 1/2x
Y
X
constant of variation =
slope =
3

4. Lesson 3­4.notebook November 05, 2012
Suppose y varies directly as x. Write a direct variation equation that relates x and
y. Then solve.
C) If y = 72 and x = 8, find y when x = 10
4

5. Lesson 3­4.notebook November 05, 2012
D) If y = 14 and x = 98, find y when x = ­28
5