cos (180/5)* cos(360/5)=?
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cos(180/5)*cos(360/5)=?cos(180/5)*cos(360/5)=?cos(180/5)*cos(360/5)=?cos(180/5)*cos(360/5)=cos36*cos
cos (180/5)* cos(360/5)=?
cos (180/5)* cos(360/5)=?
cos (180/5)* cos(360/5)=?
cos (180/5)* cos(360/5)
=cos 36* cos72
=cos 36*sin 36*cos72/sin 36
=1/2sin72*cos72/sin 36
=1/4sin144/sin 36
=1/4sin36/sin 36
=1/4
1/4
原式=cos36*cos72=cos36*(2*cos36*cos36-1)=2*cos36*cos36*cos36-cos36
cos36=cos0.2π=0.8090169943749474 下面的你自己会算了吧？给分吧 呵呵
cos (180/5)* cos(360/5)=?
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cos(180-A)=?
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