PGF/TikZ Manual

The TikZ and PGF Packages
Manual for version 3.1.9a

Part III TikZ ist kein Zeichenprogramm

by Till Tantau

(-tikz- diagram)

\usetikzlibrary {angles,calc,quotes}
\begin{tikzpicture}[angle radius=.75cm]

\node (A) at (-2,0) [red,left] {$A$};
\node (B) at ( 3,.5) [red,right] {$B$};
\node (C) at (-2,2) [blue,left] {$C$};
\node (D) at ( 3,2.5) [blue,right] {$D$};
\node (E) at (60:-5mm) [below] {$E$};
\node (F) at (60:3.5cm) [above] {$F$};

\coordinate (X) at (intersection cs:first line={(A)--(B)}, second line={(E)--(F)});
\coordinate (Y) at (intersection cs:first line={(C)--(D)}, second line={(E)--(F)});

(A) edge [red, thick] (B)
(C) edge [blue, thick] (D)
(E) edge [thick] (F)
pic ["$\alpha$", draw, fill=yellow] {angle = F--X--A}
pic ["$\beta$", draw, fill=green!30] {angle = B--X--F}
pic ["$\gamma$", draw, fill=yellow] {angle = E--Y--D}
pic ["$\delta$", draw, fill=green!30] {angle = C--Y--E};

\node at ($ (D)!.5!(B) $) [right=1cm,text width=6cm,rounded corners,fill=red!20,inner sep=1ex]
When we assume that $\color{red}AB$ and $\color{blue}CD$ are
parallel, i.\,e., ${\color{red}AB} \mathbin{\|} \color{blue}CD$,
then $\alpha = \gamma$ and $\beta = \delta$.