## Calculus (3rd Edition)

Circle in the xz-plane of radius $1$ centered at $(0,0,4)$
We put $$x=\sin t,\quad y=0, \quad z=4+\cos t$$ hence we get $$x^2+(z-4)^2= \sin^2t+\cos^2t=1.$$ Which is a circle in the xz-plane of raduis $1$ centered at $(0,0,4)$.