Hello,

As far as I know, critical points are the point in which the gradient equals zero or not defined. In the following function$\displaystyle Z=X(1+Y)^{1/2}+Y(1+X)^{1/2}$, the gradient is not defined for all $\displaystyle X\leq-1$ or $\displaystyle Y\leq-1$. How do I prove that only (-1,-1) is an extreme point (maximum)?

Thanks in advance,

Michael