Consider the following function:
f (x , y , z ) = x 2 + y 2 + z 2 − x y − y z + x + z
(a) This function has one critical point. Find it.
(b) Compute the Hessian of f , and use it to determine whether
the critical point is a local man, local min, or neither?
(c) Is the critical point a global max, global min, or neither?
Justify your answer.