Gaokao Math Practice Question
6. (5 分) 若 $\tan \theta=\frac{1}{3}$, 则 $\cos 2 \theta=(\quad)$
- A.$-\frac{4}{5}$
- B.$-\frac{1}{5}$
- C.$\frac{1}{5}$
- D.$\frac{4}{5}$
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