In each of the following cases find the gradient vector and the hessian metrix of each function f (x, y).

a). f (x, y)= 3x + 4y^3

b). f (x, y)= x^3 In y+6x^2y^3+e^2x y

c). f (x, y)= (x^2 + 4y^2)^-1/2

d) f (x, y)= (x +4y)(e^-2x + e^-3y)