Find the gradient and hessian of each of the following functions and use the hessians to check whether the functions are convex. (b) f: R2 R given by f(x,y) = x - 2xy - y6. (c) f: R R given by f(21, 22, 23) = cos(1) + 22 eigenvalues of the hessian). (you may use a computer to find the