作业帮两角差的余弦的计算题、、急...
来源：学生作业帮 编辑：拍题作业网作业帮 分类：数学作业 时间：2024/04/29 05:55:23
两角差的余弦的计算题、、急...
cos105°=
cos165°=
cos（5π/12）=
cos（17π/12）=
cos70°cos40°+sin70°sin40°=
cos100°cos20°-sin100°sin20°=
cos105°=
cos165°=
cos（5π/12）=
cos（17π/12）=
cos70°cos40°+sin70°sin40°=
cos100°cos20°-sin100°sin20°=
cos105°= cos(45°+60°)=cos45°cos60°-sin45°*sin60°=√2/4-√6/4=（√2-√6）/4
cos165°=cos(45°+120°)=cos45°cos120°-sin45°sin120°=-√2/4-√6/4=-(√2+√6)/4
cos（5π/12）= cos(π/6+π/4)=cosπ/6cosπ/4-sinπ/6sinπ/4=√6/4-√2/4=(√6-√2)/4
cos（17π/12）=cos(π+5π/12)=-(√6-√2)/4
cos70°cos40°+sin70°sin40°
= cos(70°-40°)=√3/2
cos100°cos20°-sin100°sin20°
=cos(100°+20°)=-1/2
cos165°=cos(45°+120°)=cos45°cos120°-sin45°sin120°=-√2/4-√6/4=-(√2+√6)/4
cos（5π/12）= cos(π/6+π/4)=cosπ/6cosπ/4-sinπ/6sinπ/4=√6/4-√2/4=(√6-√2)/4
cos（17π/12）=cos(π+5π/12)=-(√6-√2)/4
cos70°cos40°+sin70°sin40°
= cos(70°-40°)=√3/2
cos100°cos20°-sin100°sin20°
=cos(100°+20°)=-1/2