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2. （5 分 $) \sin 20^{\circ} \cos 10^{\circ}-\cos 160^{\circ} \sin 10^{\circ}=(\quad ）$

Gaokao · Math · previous-year question

  1. A.$\frac{\sqrt{3}}{2}$
  2. B.$\frac{\sqrt{3}}{2}$
  3. C.$-\frac{1}{2}$
  4. D.$\frac{1}{2}$correct

Answer

D. $\frac{1}{2}$

Explanation

解: $\sin 20^{\circ} \cos 10^{\circ}-\cos 160^{\circ} \sin 10^{\circ}$ $=\sin 20^{\circ} \cos 10^{\circ}+\cos 20^{\circ} \sin 10^{\circ}$ $=\sin 30^{\circ}$ $=\frac{1}{2}$ 故选: D.

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