求cos1°+cos2°+cos3°+...+cos178°+cos179°的值（这里的数字都是度数比如1°）

cos1°+cos2°+cos3°+...+cos178°+cos179°
=（cos1°+cos179°）+（cos2°+cos178°）+……+（cos89°+cos91°）+cos90°
=（cos1°-cos1°）+（cos2°-cos2°）+……+（cos89°-cos89°）+cos90°
=cos90°
=0