作业帮cos24°cos54°－sin24°cos144°急!
来源：学生作业帮助网 编辑：作业帮 时间：2024/05/05 18:27:02
cos24°cos54°－sin24°cos144°急!
cos24°cos54°－sin24°cos144°急!
cos24°cos54°－sin24°cos144°急!
cos144°=cos(90°+54°）=-sin54°
则
cos24°cos54°－sin24°cos144°=cos24°cos54°+sin24°sin54°
由cosacosb+sinasinb=cos(a-b)得
原式=cos(54°-24°)
=cos30°
=√3/2
cos24°cos54°－sin24°cos144°
= cos24°cos54°+sin24°cos36°
= cos24°cos54°+sin24°sin54°
=cos(24°-54°)
=cos(-30°)
=cos30°
=√3/2
cos24°cos54°－sin24°cos144°=?
cos24°cos54°－sin24°cos144°急!
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