1+cos2x=?答案是2cos^2 x.怎么算?
问题描述：
1+cos2x=?答案是2cos^2 x.怎么算?
答
cos2x=cos(x+x) 所以cosx^2-sinx^2=cos2x 两边+1 cosx^2+1-sinx^2=cos2x 2cosx^2=1+cos2x cosx^2=(1+cos2x)/2所以1+cos2x=2cos^2 x