4. Show that the following two functions have two local maxima but no other extreme points. Use a graphing program to create a graph that shows the two local maxima of each function. (Source: Ira Rosenholtz, Mathematics Magazine, Feb 1987) (a) f(x, y) = -(22 -1)2 - (22 - ey)2 (b) f(x, y) = 4x2ey - 2.x4 - ety