Show thatf(x,y)= $\displaystyle \sqrt{x^2+ y^2}$ has one critical point P and that f is nondifferentiable at P. Is P a saddle point, minimum, or maximum?

So I found f_{x }= $\displaystyle \frac {2x} {\sqrt {x^2 + y^2}}$ and f_{y}= $\displaystyle \frac {2y} {\sqrt {x^2 + y^2}}$ and I tried some algebraic gymnastics to try and solve for critical points but unfortunately I'm just flat out stuck

Thanks

Anthony