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.