$f(z)$ = $\sin x + \sin y + \sin (x+y)$ in the region $0 ≤ x ≤ \frac{π}{2}$ , $0 ≤ y ≤ \frac{π}{2}$
What is the best way to resolve this issue?
Should I take the first derivative, find the zeros, and test the value of the function against the other points?