一道高中三角函数题cos1度+cos2度+cos3度+.....
c1度+cos2度+cos3度+......+cos99度+cos180度=
根据cosX=-cos（180-X)可得cos1°=-cos179°，cos2°=-cos178°...可知cos1°+cos2°...+cos179°+cos180°=cos90°+cos180°=-1