Question

Eliminate the parameter.

x = 3 cos t, y = 3 sin t

Answer 1

will i need identities for this

Answer 2

This one is somewhat trickier. You have to use the Pythagorean identity:
\[\cos^2\theta+\sin^2\theta=1\]
Notice that \(x^2=9\cos^2t\) and \(y^2=9\sin^2t\), and that adding them together you have
\[x^2+y^2=9\left(\cos^2t+\sin^2t\right)\]
Utilizing the identity, you get
\[x^2+y^2=9\]