S : f(x, y) = 5x y - 2xy +x ty -2. 4. Use your answer from the previous problem to approximate f(1.01, 0.99). 5. (See Example 4.24) Show that the following function is differentiable f (x, y) = 3x2y - y. 6. Do the following problems from 4.5: (217, 223, 233) 7. Do the following problems from 4.6: (263, 273, 293, 297) O FI 199+ WW hp