怎么证明sin^2(a)+cos^2(a+30)+sinacos(a+30)=3/4请告诉我答案及解题过程!谢谢!
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![怎么证明sin^2(a)+cos^2(a+30)+sinacos(a+30)=3/4请告诉我答案及解题过程!谢谢!](/uploads/image/z/665954-26-4.jpg?t=%E6%80%8E%E4%B9%88%E8%AF%81%E6%98%8Esin%5E2%28a%29%2Bcos%5E2%28a%2B30%29%2Bsinacos%28a%2B30%29%3D3%2F4%E8%AF%B7%E5%91%8A%E8%AF%89%E6%88%91%E7%AD%94%E6%A1%88%E5%8F%8A%E8%A7%A3%E9%A2%98%E8%BF%87%E7%A8%8B%21%E8%B0%A2%E8%B0%A2%21)
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怎么证明sin^2(a)+cos^2(a+30)+sinacos(a+30)=3/4请告诉我答案及解题过程!谢谢!
怎么证明sin^2(a)+cos^2(a+30)+sinacos(a+30)=3/4
请告诉我答案及解题过程!谢谢!
怎么证明sin^2(a)+cos^2(a+30)+sinacos(a+30)=3/4请告诉我答案及解题过程!谢谢!
左边=(1-cos2α)/2+(1+cos(2α+60°))/2+sinαcos(α+30°)
=1+1/2[cos(2α+60°)-cos2α]+1/2[sin(2α+30°)-1/2]
=3/4-1/2cos2α+1/2[sin(2α+30°)-sin(2α-30°)]
=3/4-1/2cos2α+1/2[2cos2αsin30°]
=3/4
=右边
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