Consider the function (, ) = 4 − 2 − . a. Find . And . b. What is the equation of the tangent plane at the point (1, −2, −14)? How do you know that the function is differentiable (has a tangent plane) at this point? Confirm your answer using Geogebra. c. What are the critical points of ? d. Determine if has a local max, local min or saddle point at each critical point using the 2nd derivative test when possible. e. Where does have a horizontal tangent plane?