Let f (x,y) = 100 + 10x + 25y - x2 - 5y2.
(A) Describe the cross sections of the surface z = f(x, y) produced by cutting it with the planes y = 0, y = 1, y = 2, and y = 3.
(B) Describe the cross sections of the surface in the planes x = 0, x = 1 , x = 2, and x = 3.
(C) Describe the surface z = f(x, y).