Find the local maximum and minimum values and saddle point(s) of
the function. If you have three-dimensional graphing software,
graph the function with a domain and viewpoint that reveal all the
important aspects of the function. (Enter your answers as a
comma-separated list. If an answer does not exist, enter DNE.) f(x,
y) = y2 − 8y cos x, −1 ≤ x ≤ 7 local maximum value(s) local minimum
value(s) saddle point(s) (x, y, f) =