Parametrizing intersection I'm working on a question that require parametrizing some curves:

C is the curve of intersection of the hyperbolic paraboloid $z = y^2 − x^2$ and the cylinder 
  $x^2 + y^2 = 1$ oriented counterclockwise as viewed from above. Let $x$ and $y$ be in terms of $t$ where $0 ≤ t ≤ 2π$.

I thought it was quite obvious that the parametrization is $\cos{t}, \sin{t}, \sin^2{t} - \cos^2{t}$, but no, apparently it's wrong:

What am I missing here?

Your answer is correct.
Try entering the answer $\bigl(\sin t, \cos t, -\cos 2t \bigr)$. This answer is equivalent to yours, but maybe the computer system is too dumb to realize this.
