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F^{\prime}=\frac{1}{2}\left(L^{2}-100\right)^{-1 / 2} \frac{\mathrm{d}\left(\mathrm{L}^{2}-100\right)}{\mathrm{dt}}=\frac{2 \mathrm{~L} \cdot \mathrm{L}^{\prime}}{2 \sqrt{\mathrm{L}^{2}-100}}