求cos87°cos432°-sin93°cos198°的值
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/07/26 10:25:03
求cos87°cos432°-sin93°cos198°的值
![求cos87°cos432°-sin93°cos198°的值](/uploads/image/z/20076841-1-1.jpg?t=%E6%B1%82cos87%C2%B0cos432%C2%B0-sin93%C2%B0cos198%C2%B0%E7%9A%84%E5%80%BC)
cos87°cos432°-sin93°cos198°
=cos87°cos(360°+72°)-sin(180°-87°)cos(180°+18°)
=cos87°cos72°+sin87°cos18°
=cos87°cos72°+sin87°sin72°
=cos(87°-72°)
=cos15°
=(√6+√2)/4
=cos87°cos(360°+72°)-sin(180°-87°)cos(180°+18°)
=cos87°cos72°+sin87°cos18°
=cos87°cos72°+sin87°sin72°
=cos(87°-72°)
=cos15°
=(√6+√2)/4