已知sin(a-π/4)=-根号2/10,0扫码下载作业帮拍照答疑一拍即得
问题描述：
已知sin(a-π/4)=-根号2/10,0 扫码下载作业帮
拍照答疑一拍即得
答
由a范围
则cos(a-π/4)>0
sin²+cos²=1
所以cos(a-π/4)=7√2/10
cosa=cos(a-π/4+π/4)
=cos(a-π/4)cosπ/4-sin(a-π/4)sinπ/4
=4/5