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) = 6 sin(x) sin(y), −π <
x < π, −π < y < π
local maximum value(s)
local minimum value(s)
saddle point(s)