I have to find the critical points of this function of two variables [tex]\\f(x,y)=x^4+y^4-16(x+y)^2\\[/tex], for this we use the gradient method which equals to ZERO the first partial derivatives. After clearing both equations we should find the following points: P (__, 0), Q (4, __), R (4, __) My problem is that I cannot clear the following equations:

[tex]\\1) 4x^{3} -32x -32y = 0\\2) 4y^{3} -32x-32y = 0[/tex]
Is there any way to deal with these equations of degree n?