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问题: 一道高中三角函数题

cos1度+cos2度+cos3度+......+cos99度+cos180度=

解答:

根据cosX=-cos(180-X)可得cos1°=-cos179°,cos2°=-cos178°...可知cos1°+cos2°...+cos179°+cos180°=cos90°+cos180°=-1