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1.sin（90°+33°）为什么=cos33°?2.sin63°sin123°+cos117°sin33°=?
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1.sin（90°+33°）为什么=cos33°?2.sin63°sin123°+cos117°sin33°=?
▼优质解答
答案和解析
1.
sin(π/2+α)=sin(π/2)cosα+cos(π/2)sinα=cosα
2.
sin63°sin123°+cos117°sin33°
=sin(180°-63°)sin(90°+33°)+cos117°sin33°
=sin117°cos33°+cos117°sin33°
=sin(117°+33°)
=sin150°
=sin30°
=1/2
sin(π/2+α)=sin(π/2)cosα+cos(π/2)sinα=cosα
2.
sin63°sin123°+cos117°sin33°
=sin(180°-63°)sin(90°+33°)+cos117°sin33°
=sin117°cos33°+cos117°sin33°
=sin(117°+33°)
=sin150°
=sin30°
=1/2
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