\[R_{-a}\left(\mathbf{b};\mathbf{z}\right)=\frac{2}{\mathrm{B}\left(b_{1},b_{2}%
\right)}\int_{0}^{\pi/2}{(z_{1}{\cos}^{2}\theta+z_{2}{\sin}^{2}\theta)}^{-a}\*%
(\cos\theta)^{2b_{1}-1}(\sin\theta)^{2b_{2}-1}\,\mathrm{d}\theta,\]