详细步骤 谢谢
1个回答
2014-08-15
展开全部
cos24°cos36°-cos66°cos54°
=cos24°cos36°-cos(90°-24°)cos(90°-36°)
=cos24°cos36°-sin24°sin36°
=cos(24°+36°)
=cos60°
=1/2
=cos24°cos36°-cos(90°-24°)cos(90°-36°)
=cos24°cos36°-sin24°sin36°
=cos(24°+36°)
=cos60°
=1/2
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