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August 22, 2014

August 22, 2014

Posted by **Mark Russel** on Saturday, October 17, 2009 at 10:09pm.

1. a is directly proportional to b.If a=15,then b=9

2. m varies directly as n.If n=2/3,then m=1/4

3. T varies as the square root of L. If L=81,then T=10

4.r varies directly as the square of t. If t=16,then r=6.

5. y varies as the cube foot of x. If x=27,then y=2.

6. y is directly proportional to x. If y=15 when x=4,find y when x=5.

7. m varies directly as n. If m= -6 when n=2,find m when n=-3

8. The square of x varies directly as the cube of y. When x=2,y=4,find y when x=8

- Math -
**Reiny**, Saturday, October 17, 2009 at 10:57pmWhat do you want for #1 - 5 ?

Are you finding the constant of variation or what?

I will do one of them, #4

r varies directly as the square of t. ---> r = kt^2

when t=16, r=6

6 = k(16)^2

6 = 256k

k = 6/256 = 3/128

so r = (3/128)t^2

#8.

The square of x varies directly as the cube of y. ---> x^2 = ky^3

when x=2, y=4

4 = k(64)

k = 4/64 = 1/16

so x^2 = (1/16)y^3

when x = 8

64 = (1/16)y^3

y^3 = 1024

y = 1024^(1/3) = 8cuberoot(2)

Do the others the same way.

let me know what you got for the rest.

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