cos10+cos130+cos250

分类: 作业答案 • 2022-07-25 10:28:23

问题描述：

cos10+cos130+cos250

答

=cos10-(cos50+cos70)
=cos10-[cos(60-10)+cos(60+10)]
=cos10 -(cos60cos10+sin60sin10+cos60cos10-sin60sin10)
=cos10-cos10
=0