1. 4.6
Write and graph direct variation
equations

2. Direct variation
• Two variables x and y show direct
variation provided y=ax and a does not
equal zero. (y varies directly with x)
• a is called the constant of variation
– Example: y=5x
• Any equation that can be rewritten as y=ax
represents direct variation.
– Example: 2x-3y=0

3. Determine whether each equation
represents direct variation and
identify the constant of variation:
• -x+y=1
• 2x+y=0
• 4x-5y=0

4. Graphing direct variation equations

5. Graph direct variation equations
xy
3
2
=
y
x

6. Graph direct variation equations
xy 3−=
y
x

7. Identify the constant of variation
• y=ax
– Substitute coordinates
– Solve for a
– Rewrite equation
• What is y if x is 3?
• What is y if x is 600?
y
x
(-2, 4)

8. Use direct variation
s
w

9. Use direct variation

10. Use direct variation