I am confused over a few problems I solved/ tried to solve for a problem set.

My 1st question is:

Simplify x ^ -2 / x^-2+ y^-2

The simplified version I got was

x^2 + y^2 / x^2

I am not to sure if this is correct if anyone can verify it that would greatly help.

My next question is

Consider a cube with legnth of the side equal to s, then write a function of s whose value is the volume of a cube.

I believe the correct answer is

f(x) = s^3

but I am also not to sure about the answer to this one.

My last question is if I am solving the equation for a circle and I have

4x^2 + 16x + 64 + 4y^2 - 8y + 16 = Root 78

I cannot factor out the terms for x and y to end up with the normal circle equations. Can I use the quadratic formula to solve for the center and radius?

Thanks for any help anyone may provide.