
Originally Posted by
noppawit
I'm wondering that I did this problem correct, or not.
Find the local maximum and minimum values and saddle point(s) of the function [tex]f(x,y) = 1-x^2-y^2[/+2xymath]
$\displaystyle \nabla f = 0$
$\displaystyle \nabla f =<\frac{\partial f }{\partial x },\frac{\partial f }{\partial y }>=<2y-2x,2x-2y>$
Then, I got x=y. After that, I tried to find $\displaystyle D = fxx*fyy-f^2xy$
I've got 0 from D. Therefore, I concluded D=0, no conclusion.
Am I right? Is there anything wrong?
Thank you.