解答

Choosen As Best Answer

cos1°+cos2°+cos3°+.......cos90°.......+cos177°+cos178°+cos179°+cos180°
=cos1°+cos2°+cos3°+.....cos90°.......
-cos3°-cos2°-cos1°+cos180°
=cos90°+cos180°=0-1=-1

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