Definition. A critical point of a function f = f(x, y) is a point in the domain of f at which fr(xo, yo) = 0 and fy(ro, yo) = 0, or such that one of f(ro, yo) or fy(ro, yo) fails to exist. 1. Find the critical points of each of the following functions. (a) f(x, y) = 2+x² + y² (b) f(x,y) = 2+x² - y2 (c) f(x, y) = 2x+x²- y² (d) f(x, y) = |x|+y =1 (e) f(x, y) = 2xy -4x+2y-3