5. (2 points) Use a tangent hyperplane approximation to estimate \\ (3.02)2 + (1.97)2 + (5.99)2. 6. (6 points) Find all the local maxima, local minima, and saddle points of the given functions. (a) f(x, y) = -x2 + 2xy - 6x - 242 + 8y-4 (b) f(x, y) = 223 + 2y3 - 922 + 3y2 -12y (c) f(x, y) = 3x2 + 6xy - 23 + 12y2 -2