1+cos2x=?答案是2cos^2 x.怎么算?

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1+cos2x=?答案是2cos^2x.怎么算?1+cos2x=?答案是2cos^2x.怎么算?1+cos2x=?答案是2cos^2x.怎么算?cos2x=cos(x+x)所以cosx^2-sinx^

1+cos2x=?答案是2cos^2 x.怎么算?
1+cos2x=?答案是2cos^2 x.怎么算?

1+cos2x=?答案是2cos^2 x.怎么算?
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