4.2 Slope & Direct Variation Divide (the pattern) If y varies directly as x then the pattern is If y varies directly as x2,
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.
You can graph these too! y = 3x
Try Example #1 & 2A, 2B, 2D Check your Progress 1. ¼; ¼ 2A. 2B. 2D.
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
y varies directly as x. If y = 3 when x = 15, find y when x = -25. Cross Multiply y = -5
6 lbs. of sugar costs $2. 00. At that rate, how much will 40 lbs 6 lbs. of sugar costs $2.00. At that rate, how much will 40 lbs. of sugar cost? Reduce fraction 40 = 3x 3 3 x=$13.33
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