Answer
(a) See the graph.
(b) $x+y=1,~~0\leq x\leq1$
Work Step by Step
(a)
$x=cos^2t$ and $y=sin^2t$ are period functions. The maximum and the minimum value of $x=cos^2t$ are $1$ and $0$, respectively. In these points occurs a change of direction.
(b)
$x=cos^2t$
$y=sin^2t$
$cos^2t+sin^2t=1$
$x+y=1$
