9. (5 points) Find an equation of the plane tangent to the surface S at the point (1, 1, 7), where S is defined by S : f(x, y) = 2x y + 5xy - 512 + 7y - 2. Furthermore, use the result to approximate the value of f(1.01, 0.998). 10. Let C be the curve defined by C : 7x213 - 5ry + 4.x + 2y = 10. (a) (4 points) Find dy/dr at the point (-1, 1) using implicit differentation. (b) (3 points) Find dy/dar at the point (-1, 1) using partial derivatives. (c) (3 points) Find an equation of the line tangent to the C at the point (-1, 1). o search O Hi 99 + B F 83"F ~