Let f R2 R be the function defined by f(x,y) = 2(y-2)3 (x-1)+(y-2)2 if (x, y) (1,2), 0. if (x, y) = (1,2). a. Evaluate f. (0,0) and f,(0,0), if exist. Show your work. b. Evaluate f,(1,2) and f,(1,2), if exist. Show your work. c. Determine whether or not the function f(x, y) is differentiable at the point (1,2). Show your work.