Hello, just got done taking a test and one problem kinda confused me. 1. The problem statement, all variables and given/known data f(x,y) = e^x cos y find local min/max and saddle points 2. Relevant equations fx = e^x cos y fy = -e^x sin y 3. The attempt at a solution I answered that there were no critical points for this function and therefore no extrema. I looked at a graph of this here. To me, those sharp crevices indicate the function is not differentiable at those points. Is this correct?