4. (11 points) Consider the constant elasticity of substitution (CES) utility function U (1'1, 1:2) : (I? + 133); a) (2 points) Compute the total dierential of U with respect to Ugh-1:2 (i.e. your equation should include the terms dU: 111:1. til-1:2). b) (2 points) Use your previous answer to compute the slope of an indifference curve for some consumption bundle (171,122). c) (2 points) Instead: use the equation 5 = (:6; | 1.3% to express 1:: explicitly as function of 331 and U. (1) (2 points) Use your answer in c) to compute the derivative i? explicitly. e) (3 points) Prove that your answers in b) and d) are the same. dim) {1x1 d} Compute the derivative explicitly: X3 : U\" X? Apply the chain rule : A I: Step4: lag) : (A) x (UH _ Elli} n X (n >