ECON 2050 SEMESTER 2 2023 Quiz 2
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ECON 2050
SEMESTER 2 2023
Quiz 2
Due on Blackboard on Friday 27 October 2023 at 16:00
Question 1 (15 marks)
Prove that S = {(x, y) 2 R2 : 2x2 — y 3 }is a convex set by directly verifying that
S satisfies the definition of a convex set.
Question 2 (15 marks)
Let D be a convex subset of Rn. If f : D ! R is a concave function and k 2 R, then the upper contour set S = fx 2 D : f(x) ≥ kg is a convex set. Using this theorem, show that if a 2 [ — 1, 1] and b 2 R, then the following set M, is convex. M = f(x,y, z) 2 (0, 2) 根 R2 : ln x — 2y2 — axy ≥ 0, x + by + z 0g
Question 3 (15 marks)
Consider the function f : R2 ! R, (x, y) |! — 6x4 — 2 + 6xy. Find all critical points off and classify each critical point as A) a local maximum, B) a local minimum or C) a saddle point. Show each of your steps.
Question 4 (20 marks)
For all possible values of a and c, solve the constrained maximization problem
max 2xy + 2z s.t. x2 + y2 = 8, 2ax + 2ay + 2z = 2c
(x,y,z)=R3
using the Lagrange approach. You may assume that the constraint set is compact without proof. Explain each of your steps.
Question 5 (20 marks)
Consider the following maximization problem:
max — (x + 1)2 — (y — 4)2 s.t. x + (y — 3)3 0, y ≥ 2x2 , x ≥ 0, y ≥ 0
(x;g)=R2
You may use without proof the fact that this problem has a solution.
(a) Determine and explain whether any points of the constraint set violate the non- degenerate constraint qualification of the Kuhn-Tucker theorem. (7 marks)
(b) Solve this problem by applying the Kuhn-Tucker theorem. (13 marks)
Question 6 (15 marks)
Consider the following maximization problem:
max —x2 — y2 s.t. — x — y —4, y + 2x 5
(x;g)=R2
(a) Can you apply the Extreme Value Theorem to conclude that this problem does have a solution? Explain why or why not. (2 marks)
(b) Is the objective function convex and/or concave? Prove your answer. (2 marks)
(c) Is the constraint set convex? You do not need to prove your answer. (1 mark)
(d) Solve this problem by applying the Kuhn-Tucker theorem. Carefully explain each of your steps. You may use without proof the fact that all points of the constraint set satisfy the non-degenerate constraint qualification. (8 marks)
(e) Without solving any other maximization problem, estimate whether the function f : R2 ! R, (x, y) '! — x2 — y2. attains a higher value in the set C1 = f(x, y) 2 R2 : —x — y —3, y +2x 5g or in the set C2 = f(x, y) 2 R2 : —x — y —4, y +2x 6g. (2 marks)
2023-10-30