Use the first principles definition of the derivative to determine if the following function is differentiable at x = 4. NOTE: The function is continuous at X = 4. [A: /4] x54 f(x) = 15-x 5-x, x>4Differentiate each of the following functions. Express your answers as stated. [KU: a) f(x) = x(2 - x)3(3x + 2)4 Do NOT simplify! (3 marks) b) y= (x2+1) + V1-2x Express your answer in the simplest factored form (4 marks)