Nebenwinkel ergänzen sich zu ${180}^{\circ }180^\backslash circ$.

$\begin{array}{c}\alpha +2\cdot \alpha ={180}^{\circ }\\ \alpha ={60}^{\circ }\end{array}\backslash def\backslash arraystretch\{1.25\}\; \backslash begin\{array\}\{l\}\backslash alpha+2\backslash cdot\backslash alpha=180^\backslash circ\backslash \backslash \backslash alpha=60^\backslash circ\backslash \backslash \backslash end\{array\}$

Die Summe der Winkel in einem Dreieck beträgt ${180}^{\circ }180^\backslash circ$.

$\alpha \backslash alpha$ ist ein Stufenwinkel und es gilt

$\beta +\alpha +{90}^{\circ }={180}^{\circ }\backslash beta+\backslash alpha+90^\backslash circ=180^\backslash circ$

$\begin{array}{c}\beta +{60}^{\circ }+{90}^{\circ }={180}^{\circ }\\ \beta ={30}^{\circ }\end{array}\backslash def\backslash arraystretch\{1.25\}\; \backslash begin\{array\}\{l\}\backslash beta+60^\backslash circ+90^\backslash circ=180^\backslash circ\backslash \backslash \backslash beta=30^\backslash circ\backslash end\{array\}$

Das Winkelmaß $\beta \backslash beta$ ist ${30}^{\circ }30^\backslash circ$.