Drawing a triangle

Question

I want to draw a triangle (with the package TikZ). I don't know how to draw the line, which links the BC points. I know I have to use these commands: +(a,b), ++(a,b), (a:b|-c,d). Unfortunately I cannot use any of these commands, so please explain, how to use these commands and what do they mean.

Please, introduce the commands in detail. And also, I need the line, which links the points AB. I do not need the points and the "=45°" in my LaTeX document.

Answer 1

I probably do not know tikz more than you (being a MetaPost user), but out of curiosity I've just consulted the quite elegant tutorial at the beginning its documentation (p. 28-93), and I've come to this result:

\documentclass[12pt, border=5mm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw (0,0) node[anchor=north]{$A$}
  -- (4,0) node[anchor=north]{$C$}
  -- (4,4) node[anchor=south]{$B$}
  -- cycle;
\end{tikzpicture}
\end{document}

This tutorial has probably the answers to most of your questions: a must-read.

Answer 2

After five years ...

• For starting point is used @Franck Pastor nice answer (+1)
• instead nodes are employed coordinates with labels
• added is angle value (using siunitx)

\documentclass[12pt, tikz, border=5mm]{standalone}
\usetikzlibrary{angles,
                quotes}
\usepackage{siunitx}

\begin{document}
\begin{tikzpicture}[
my angle/.style = {draw, fill=teal!30,
                   angle radius=7mm, 
                   angle eccentricity=1.1, 
                   right, inner sep=1pt,
                   font=\footnotesize} 
                   ]
\draw   (0,0) coordinate[label=below:$A$] (a) --
        (4,0) coordinate[label=below:$C$] (c) --
        (4,4) coordinate[label=above:$B$] (b) -- cycle;
\pic[my angle, "$\alpha=\SI{45}{\degree}$"] {angle = c--a--b};
    \end{tikzpicture}
\end{document}