Gaokao Math Practice Question
11.已知 $a \in\left(0, \frac{\pi}{2}\right), 2 \sin 2 \alpha=\cos 2 \alpha+1$, 则 $\sin \alpha=$
- A.$\frac{1}{5}$
- B.$\frac{\sqrt{5}}{5}$
- C.$\frac{\sqrt{3}}{3}$
- D.$\frac{2 \sqrt{5}}{5}$
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