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2014-03-25T23:41:31+02:00


cos30= √3 / 2

cos 60= 1/2

cos (90+α)= -sin α

cos120=cos (90+30)=-sin 30= - 1/2

cos150 = cos (90+60)= - sin 60 = - √3/2

⇒cos 30 +cos60 +cos 120 +cos 150 = √3/2 +1/2 - 1/2 - √3/2 = 0

2014-03-26T00:04:11+02:00