Use a graphing device as in Example 4 (or Newton’s method or solve numerically using a calculator or computer) to find the critical points of f correct to three decimal places. Then classify the critical points and find the highest or lowest points on the graph, if any.

f(x, y) = 20e^-x2-y2 sin 3x cos 3y, |x| < 1, | y | < 1