Find the local maximum and minimum values and saddle point(s) ofthe function. If you have three-dimensional graphing software,graph the function with a domain and viewpoint that reveal all theimportant aspects of the function. (Enter your answers as acomma-separated list. If an answer does not exist, enter DNE.)
1)f(x, y)= 6ycos(x),    0 ≤x ≤ 2π
2)f(x, y) =y2 − 6ycos(x),    −1 ≤x ≤ 7
3)f(x, y) = 6 sin(x) sin(y),     −π< x < π,     −π < y < π
