Answer
See answer.
Work Step by Step
a. We know that P = IV, so if power P is delivered using voltage V, the current I=P/V.
This current passes through the transmission line of resistance R. The power lost in the wire is $I^2R$ due to heating of the wire.
This transmission loss is $I^2R=(\frac{P}{V})^2R=\frac{P^2R}{V^2}$ which was to be shown.
b. The transmission loss is inversely proportional to the square of V, so V should be as large as possible.
