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\begin { equation } \begin{array}{l}{\text { 39. } \frac{\sin A-\sin B}{\cos A+\cos B}+\frac{\cos A-\cos B}{\sin A+\sin B}=0} \\ {\text { 40. } \frac{\tan A+\tan B}{\cot A+\cot B}=\tan A \cdot \tan B}\end{array} \end { equation } |
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