Find the rectangular equation of the curve whose parametric equations are given.

1.x=-cost t, y= sin t

2. x=-sin 2t

y=2 cos 2t

Now I am kind of confused what to for with the the "2t"

For example on number 2 I did

2 cos 2t=y

cos2t=y/2 Would I do know square it but while I would get y^2/4 on one side what would I do on the "other side"?