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.