化简cos78°cos18°+sin18°sin102°?
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发布时间：2024-10-24 07:40
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热心网友
时间：2024-10-25 09:49
cos78°cos18°+sin18°sin102°
=cos78°cos18°+sin18°sin(180°-78°)
=cos78°cos18°+sin78°sin18°
=cos(78°-18°)
=cos60°
=1/2
