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cos(180/11)cos(360/11)cos(540/11)cos(720/11)cos(900/11)
题目详情
cos(180/11)cos(360/11)cos(540/11)cos(720/11)cos(900/11)
▼优质解答
答案和解析
原式等于｛sin（180/11）cos（180/11）cos(360/11)cos(540/11)cos(720/11)cos(900/11)｝/sin(180/11)=｛1/8sin（1440/11)cos(540/11)cos(900/11)}/sin(180/11)
={1/8sin(180-540/11)cos(540/11)cos(90-90/11)}/sin(180/11)
={1/16sin(1080/11)sin(90/11)}/sin(180/11)
={1/16cos(90/11)sin(90/11)}/sin(180/11)
=1/32
={1/8sin(180-540/11)cos(540/11)cos(90-90/11)}/sin(180/11)
={1/16sin(1080/11)sin(90/11)}/sin(180/11)
={1/16cos(90/11)sin(90/11)}/sin(180/11)
=1/32
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