I know you have to find the partial derivatives but can find values for x and y to make them 0.
Full question is...

Find the critical points of the function.
f(x,y) = 2sin(x)cos(y) + cos(x)sin(y).

And determine their nature.

Think i use the Hessian rule to find their nature but again cant find the points.
Can anybody help please? cheers!