6. $\cos ^{2} \frac{\pi}{12}-\cos ^{2} \frac{5 \pi}{12}=(\quad)$
Gaokao · Math · previous-year question
- A.$\frac{1}{2}$
- B.$\frac{\sqrt{3}}{3}$
- C.$\frac{\sqrt{2}}{2}$
- D.$\frac{\sqrt{3}}{2}$
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