1. 4.2 Slope & Direct Variation
Divide (the pattern)
If y varies directly as x
then the pattern is
If y varies directly as x2,

2. y = k x Direct variation The pattern is easier to work the problems.
(This is the equation for direct variation.)
The pattern is easier to work
the problems.
k is the constant of variation.

3. You can graph these too!
y = 3x

4. Try Example #1 & 2A, 2B, 2D Check your Progress
1. ¼; ¼
2A.
2B.
2D.

5. Constant of variation = k It is the same as slope!
Find the constant of variation if y = 3 when x = 15 and then write an equation using y = kx.
Constant of variation = k
It is the same as slope!
y=k x
y=1/5 x

6. y varies directly as x. If y = 3 when x = 15, find y when x = -25.
Cross Multiply
y = -5

7. 6 lbs. of sugar costs $2. 00. At that rate, how much will 40 lbs
6 lbs. of sugar costs $ At that rate, how much will 40 lbs. of sugar cost?
Reduce fraction
40 = 3x 3 3
x=$13.33

8. Try these p. 200 #1, 3, 4, 8
1. -1/3, -1/3 3. 4.
8. y = -½x; 8
Homework #27 Practice 4.2 & Skills Practice 4.2