Cho \(\sin \alpha .\cos \left( {\alpha  + \beta }...

Câu hỏi: Cho \(\sin \alpha .\cos \left( {\alpha  + \beta } \right) = \sin \beta \) với \(\alpha  + \beta  \ne \frac{\pi }{2} + k\pi ,\,\,\alpha  \ne \frac{\pi }{2} + l\pi ,\,\,\left( {k,\,l \in Z} \right)\). Ta có:

A. \(\tan \left( {\alpha  + \beta } \right) = 2\cot \alpha \)

B. \(\tan \left( {\alpha  + \beta } \right) = 2\cot \beta \)

C. \(\tan \left( {\alpha  + \beta } \right) = 2\tan \beta \)

D. \(\tan \left( {\alpha  + \beta } \right) = 2\tan \alpha \)