Hi

Can someone tell me if i have done the following question correctly because according to the book's answers this is incorrect.

For the surface given

Find the stationary point or points and determine the nature of any such point.

because there is still i differential again

therefore i get saddle point according to the statement

Points (1,-4,-16) > 0 & g > 0

answers is (1,-2,-8) is a local minmum; (-1,-2, 8) is a saddle point

how do i find the minmum point?

P.S