multiply both sides by x

but y = x^3 so substitute

I'm not sure about the 'all values of x' part. If x = 0 then we are zeroing out both sides of the equation and that's usually a no-no.

On the other hand , the equation was true for all real values of x BEFORE i multiplied by x so even if x = 0 we get 0 = 0 which is still true.

Maybe other MHF members can provide some insightful input regarding this matter.