TeX Quellcode:

\begin{array}{rclcl} \cos(\alpha) &=& \dfrac{b}{c} & \vert & \cdot c \cr c \cdot \cos(\alpha) &=& b & \vert & : \cos(\alpha) \cr c &=& \dfrac{b}{\cos(\alpha)} \cr\cr c &=& \dfrac{4}{\cos \left( \dfrac{11 \pi}{36} \right)} \cr c & \approx & 6{,}97 \, cm \end{array}