Finding Cartesian/symmetric form using $x,y$ and $z$

Question

I am having trouble figuring out how to write a Cartesian equation for the following: \begin{align} x & = t\\ y & = 2t\\ z & = \cos t \end{align} with $0\le t \le 4\pi$. I would know how to do it if I was given only two equation, but having a third one with a trigonometric function is throwing me off.

Answer 1

Since $x=t$, for $x \in [0,4\pi]$ you get $$ \begin{cases} y = 2x \\ z = \cos x. \end{cases} $$