Gaokao Math Practice Question
11. 若 $a \in\left(0, \frac{\pi}{2}\right), \tan 2 a=\frac{\cos a}{2-\sin a}$, 则 $\tan a=(\quad)$
- A.$\frac{\sqrt{15}}{15}$
- B.$\frac{\sqrt{5}}{5}$
- C.$\frac{\sqrt{5}}{3}$
- D.$\frac{\sqrt{15}}{3}$
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