TITLE: Get polar equation from cartesian equation
QUESTION [5 upvotes]: I have this equation: $x^4 + y^4 = x^2 + y^2$ and I need to convert it to a polar one...
I have tried and the result is
$$r = \sqrt{\frac{1}{\cos^4\theta + \sin^4\theta}}$$
Is this ok?

REPLY [3 votes]: It is fine, though there is also the point $r=0$, i.e. $(0,0)$.  
Here is a picture, with the curve passing through the eight obvious points.