Find the Cartesian equation of a curve?

I've been given the curve x= acos^3(t), y= asin^3(t). I tried solving for r using x^2+ y^2= r^2, but didn't have much luck. As far as finding the angle, y/x gives me tan^3(t) and trying to take the arctan of that makes no sense at all to me. Could someone please show me all the steps?