\begin{tikzpicture}[x={(0.866cm,0.5cm)}, y={(-0.866cm,0.5cm)}, z={(0cm,1cm)}]
  \draw[->] (-1,0,0) -- (5,0,0) node[right] {$x$};
  \draw[->] (0,-1,0) -- (0,5,0) node[above] {$y$};
  \draw[->] (0,0,-1) -- (0,0,5) node[above] {$z$};

  \coordinate (A) at (0,0,0); \coordinate (B) at (4,0,0);
  \coordinate (C) at (4,4,0); \coordinate (D) at (0,4,0);
  \coordinate (E) at (0,0,4); \coordinate (F) at (4,0,4);
  \coordinate (G) at (4,4,4); \coordinate (H) at (0,4,4);

  \draw[dashed] (A) -- (B); \draw[dashed] (A) -- (D); \draw[dashed] (A) -- (E);
  \draw (B) -- (C) -- (G) -- (F) -- cycle;
  \draw (D) -- (C); \draw (E) -- (F); \draw (E) -- (H) -- (G); \draw (D) -- (H);

  \coordinate (P1) at (0,0,0);
  \coordinate (P2) at (4.33,0,0);
  \coordinate (P3) at (2.414,3.828,0);

  \draw[red, ultra thick] (P1) -- (P2) -- (P3) -- cycle;

  \node[left, xshift=-2pt] at (P1) {$A$};
  \node[right, xshift=2pt] at (P2) {$B$};
  \node[above, yshift=3pt] at (P3) {$C$};
  \fill[red] (P1) circle (2pt) (P2) circle (2pt) (P3) circle (2pt);
\end{tikzpicture}

@3d: cam(elev=35deg, azim=45deg, proj=oblique)

K = cube(size=4)
draw: K, hide=dash, thick=1.5pt

solve {
    A = (0, 0, 0)
    B = (?, 0, 0)
    C = (?, ?, 0)

    dist(A, B) == 5
    dist(B, C) == 7
    ang(C, A, B) == 30deg
    C.y == C.x^2 - 2
}

poly: A--B--C, stroke=2pt, color=#red
dot: A"A"(sw), B"B"(se), C"C"(nw)