hi everyone

having problems finding critical points for this two equation to fined the maximum,minimum or saddle points.

a) $\displaystyle x^4+y^4-4xy+1$

$\displaystyle f_x=4x^3-4y$, $\displaystyle f_y=4y^3-4x$

b) f(x,y)=$\displaystyle x^4-2x^2y+2y$

$\displaystyle f_x=4x^3-4xy$,$\displaystyle f_y=2-2x^2$

need help to find the critical points for this two equations,really hope someone can help me. really appreciate all your help & support.