(cos36°)平方+(cos72°)平方等于多少?
来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/08/29 05:53:21
(cos36°)平方+(cos72°)平方等于多少?
原式=1-sin²36+sin²18
=1+(sin18+sin36)(sin18-sin36)
=1+[sin(27-9)+sin(27+9)][sin(27-9)-sin(27+9)]
=1+(sin27cos9-cos27sin9+sin27cos9+cos27sin9)(sin27cos9-cos27sin9-sin27cos9-cos27sin9)
=1-4sin27cos9cos27sin9
=1-(2sin27cos27)(2sin9cos9)
=1-sin18sin54
=1-2sin18cos18cos36/2cos18
=1-sin36cos36/2cos18
=1-sin72/4sin72
=1-1/4
=3/4
=1+(sin18+sin36)(sin18-sin36)
=1+[sin(27-9)+sin(27+9)][sin(27-9)-sin(27+9)]
=1+(sin27cos9-cos27sin9+sin27cos9+cos27sin9)(sin27cos9-cos27sin9-sin27cos9-cos27sin9)
=1-4sin27cos9cos27sin9
=1-(2sin27cos27)(2sin9cos9)
=1-sin18sin54
=1-2sin18cos18cos36/2cos18
=1-sin36cos36/2cos18
=1-sin72/4sin72
=1-1/4
=3/4
cos36°-cos72°=?
sin72°,cos72°,sin36°,cos36°分别等于多少?
cos36度减cos72度等于多少
高中三角函数题:求COS36°-COS72°的值(要详细过程)
三角函数的,COS72°-----COS36°
高一三角函数习题cos36°-cos72°的值为_______.
高一数学必修4题化简(1)cos72*cos36(2)cos20*cos40*cos60*cos80(3)sin6*si
cos36度*cos72度=?
cos36度cos72度=?
(4Sin30°Cos72°)/(Sin18°+Cos72°)+[Cos(45°+a)]/[Cos(45°-a)]-Co
跪求大神解cos36’cos72‘=
如何直接得出cos36-cos72=1/2 cos36*cos72=1/4?