Question

write a general formula to describe the variation: x varies directly with the cube of y; x = 8 when y = -8

Answer 1

x = ky^3
substitute x = 8 and y = -8
8 = k(-8)^3
8 = -512k
k = -8/512
So x = (-8/512)y^3.

Answer 2

Thanks could you help with another one. Write a general formula to describe the variation: x varies inversely with the square of y; x = -1, when y = 5