1. ${\tan }^{-1}\left(\frac{6}{7}\right)+{\tan }^{-1}\left(\frac{1}{13}\right)$

• A. $\frac{\mathrm{\pi }}{2}$
• B. $\frac{\mathrm{\pi }}{2}$
• C. $\frac{\mathrm{\pi }}{2}$
• D. $\frac{\mathrm{\pi }}{2}$

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