Let f(x, y) = 3x +2y-10, in its domain D a) f has a local minimum. b) f is a bounded function. c) f has a local maximum. d) f has one critical point. e) If T(x, y) represents the expression of the tangent plane at the point (1, 1, f(1, 1)), then T(x,y) = f(x.y) for all (x,y).