TeX source:
\begin{array}{rclcc} a^2+b^2 &=& c^2 & \vert & -a^2 \cr b^2 &=& c^2-a^2 & \vert & \sqrt{} \cr b &=& \sqrt{c^2-a^2} \cr &\approx& \sqrt{7^2-5{,}22^2} \cr &\approx& \sqrt{21{,}7} \cr & \approx & 4{,}66 \, cm \end{array}