Gaokao Math Practice Question
6. (5 分) 已知 $\sin 2 \alpha=\frac{2}{3}$, 则 $\cos ^{2}\left(\alpha+\frac{\pi}{4}\right)=(\quad)$
- A.$\frac{1}{6}$
- B.$\frac{1}{3}$
- C.$\frac{1}{2}$
- D.$\frac{2}{3}$
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