How to plot $x^2+y^2 = 4$ and $z=2$ in 3-dimensional space in Latex

Question

I'm trying to plot $x^2+y^2 = 4$ and $z=2$ in 3-dimensional space with axes labels.

I came across pgfplot and tikz-3dplot but I could not do it.

Answer 1

This is just a circle of radius 2 in the xy plane at z=2. You can draw this circle both with tikz-3dplot and pgfplots. Here is a tikz-3dplot variant.

\documentclass[tikz,border=3mm]{standalone}
\usepackage{tikz-3dplot}
\begin{document}
\tdplotsetmaincoords{110}{70} 
\begin{tikzpicture}[tdplot_main_coords]
 \begin{scope}[canvas is xy plane at z=2]
  \draw (0,0) circle[radius=2cm];
 \end{scope}
\end{tikzpicture}
\end{document}

How this circle really is going to look depends on the view angles, which are specified by \tdplotsetmaincoords{110}{70} in the above example. You may only appreciate z=2 really after adding other stuff at different z position,