In: Economics
The utility is given to be .
(a) We have and . Also, we have or .
(b) For y satisfying , solving for y, we have or . Here y is a function of x, and . Putting it in the required equation, we have or .
(c) For , we have or or . Hence, for all values of x and y for which , we would have .
(d) We have , and hence, or , and since , we have or .
(e) For and , the answer in part-c would describe a minimum.
The graph is as below.
As can be seen, the tangency condition gives the point at P, but since the utility is concave, not convex, the condition is a minimizing one. At point P, it is the minimum of U that is tangent to the constraint.