So you know that . (Here's some advice: The answer to (a) is needed in order to answer (b). So next time, to save a poor sap like me from spending 10 seconds re-inventing the wheel, be a sport and include your answer).

The easiest approach is to sub the parametric expressions into the cartesian equation and show that you get an identity:

Consider: .

Therefore LHS = .

RHS = LHS.

Q.E.D.