1. Section 4.6 Direct Variation Direct Variation
Goal: Write & graph equations that show direct variation.

2. Direct Variation

4. k is called the variation constant. MUST PASS THROUGH ORIGIN
Direct Variation- x and y are said to vary directly if they have a relationship of y = kx where k ≠ 0.
k is called the variation constant.
MUST PASS THROUGH ORIGIN
If x varies directly with y. Write an equation that relates the variables if x = 4 and y = 16. Then find y when x = 15.
y = kx
16 = k(4)
k = 4
y = 4x
y = 4(15) = 60

6. Write a direct variation equation.
3.5 pounds of apples cost $4.20.
Write a direct variation equation.
C = kp
4.20 = k(3.5)
1.20 = k
Cost = 1.20 (# of pounds) C p p
C = 1.2p C
3.5 C = 1.2(3.5) 4.2 (3.5, 4.2)
1 C = 1.2(1) 1.2 (1, 1.2)
2 C = 1.2(2) 2.4 (2, 2.4)
0 C = 1.2(0) 0 (0, 0)

7. pounds of tomatoes
Cost
2 lbs.
$1.50
3 lbs.
$2.25
4.5 lbs.
$3.37
Is there a relationship?
Vertical Axis
Linear
Cost in $
# of pounds
Horizontal Axis

8. Homework Assignment #3
4.6 Practice A Sheet