I have function $f(x,y)=\sin(xy)$ in two variables. I found critical point $(0,0)$.
$f(x,y)$ has saddle point at $(0,0)$, because $D=f_{xx}(0,0)f_{yy}(0,0)-f_{xy}(0,0)<0$
So, I got saddle point, but what about other critical points? Please help me. Thanks in advance.