\[L_{c}=2\pi abc\int_{0}^{\infty}\frac{\,\mathrm{d}\lambda}{\sqrt{(a^{2}+\lambda%
)(b^{2}+\lambda)(c^{2}+\lambda)^{3}}}=VR_{D}\left(a^{2},b^{2},c^{2}\right).\]