[tex]\begin{array}{l}\text{Let\ x\ be\ the\ third\ side,\ then,\ by\ Pitagoras}\\\\x^{2} +5^{2} =\left(\sqrt{61}\right)^{2}\\\\\Longrightarrow x^{2} =61-25\\\\\Longrightarrow x=\sqrt{36} =6\end{array}[/tex]
