Help with second partial test please!?

C

corona7w

New member
I'm trying to find the relative max and min for a function. I take the Hessian f_xx * f_yy - f_xx^2 of all the critical points and examine the positive ones, and then look at the f_xx for each critical points to decide if it's a max or a min. But what if the f_xx is 0? How else can I decide what max or min?
 
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