\[\sum_{l}(-1)^{l+j+j_{1}+j_{2}}\begin{Bmatrix}j_{1}&j_{2}&l\\
j_{2}&j_{1}&j\end{Bmatrix}=\frac{1}{2j+1}\left(\frac{(2j_{1}-j)!(2j_{2}+j+1)!}%
{(2j_{2}-j)!(2j_{1}+j+1)!}\right)^{\frac{1}{2}},\]