Der Winkel$\alpha \backslash \; \backslash alpha\backslash$und der Winkel${30}^{\circ }\backslash \; 30^\backslash circ\backslash$sind Nebenwinkel,

Nebenwinkel ergänzen sich zu${180}^{\circ }\Rightarrow \alpha +{30}^{\circ }={180}^{\circ }\backslash \; 180^\backslash circ\backslash Rightarrow\backslash alpha+30^\backslash circ=180^\backslash circ$

$\alpha ={150}^{\circ }\backslash \; \backslash alpha=150^\backslash circ$

Der Winkel$\alpha \backslash \; \backslash alpha\backslash$und der Winkel$\beta \backslash \; \backslash beta\backslash$sind Stufenwinkel,

Stufenwinkel sind gleich groß.

$\alpha =\beta \Rightarrow \beta ={150}^{\circ }\backslash \; \backslash alpha=\backslash beta\backslash Rightarrow\backslash beta=150^\backslash circ$

Der Winkel$\beta \backslash \; \backslash beta\backslash$beträgt${150}^{\circ }\backslash \; 150^\backslash circ$