Tétraèdre avec hauteur

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[scale=2.5]
  \coordinate (A) at (0,0);
  \coordinate (B) at (2.5,0);
  \coordinate (C) at (1.8,1.2);
  \coordinate (S) at (1.2,2.5);
  % Face arrière
  \draw[dashed,gray] (A) -- (C);
  % Faces visibles
  \draw[thick] (A) -- (B) -- (C) -- cycle;
  \draw[thick] (A) -- (S);
  \draw[thick] (B) -- (S);
  \draw[thick] (C) -- (S);
  % Hauteur
  \coordinate (H) at (1.4,0.4);
  \draw[dashed,red] (S) -- (H) node[midway,right,font=\small] {$h$};
  \fill[red] (H) circle (1pt) node[below,font=\small] {$H$};
  % Labels
  \node[below left,font=\small] at (A) {$A$};
  \node[below right,font=\small] at (B) {$B$};
  \node[right,font=\small] at (C) {$C$};
  \node[above,font=\small] at (S) {$S$};
\end{tikzpicture}
\end{document}