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July 26, 2014

July 26, 2014

Posted by **Mike** on Sunday, April 18, 2010 at 9:18am.

y varies directly as the square of R. If y = 128 when R = 8, find y when R = 5.

Another one I cannot figure out:

If x varies directly as y, and x = 32 when y = 8, find x when y = 10

Help!

- Math -
**Reiny**, Sunday, April 18, 2010 at 10:06amy varies directly as the square of R

becomes ...

y = k √R , where k is a constant

let's use the given information to find k

when y = 128, R = 8, then

128 = k√8

k = 128/√8 or 16√8 or 32√2

so y = 32√(2R)

when R = 5

y = 32√10 = appr. 101.19

- Math -
**Reiny**, Sunday, April 18, 2010 at 10:06amfor the second

x = ky, try doing it the same way as the first

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