4. Find the gradient and Hessian of the following functions: (a) f : R2 -> R given by f(x1, 22) = (21 - 202) + 21 + 22. (b) f : Red -+ R given by f(x) = (a, x) 2 + (b, ac). 5. Using the results from Problem 4, determine whether the functions are convex: (a) f(x1, x2) = (21 -22) +21+22 (b) f(z) = (a, z)2 + (b, ac)