Question

This is regarding direct variation.

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!

Answer 1

y 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

Answer 2

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