• sin13°?cos17°+sin77°?sin17°= .试题及答案-填空题-云返教育

    • 试题详情

      sin13°?cos17°+sin77°?sin17°=         

      试题解答


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      解:根据诱导公式,得sin77°=cos(90°-77°)=cos13°,
      ∴sin13°?cos17°+sin77°?sin17°
      =sin13°?cos17°+cos13°?sin17°=sin(13°+17°)=sin30°=
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      故答案为:
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