问题描述: 2(sinx/2)*∑sinkx=(cosx/2)-cos(2n+1)*x/2这怎么证明 1个回答 分类:数学 2014-10-27 问题解答: 我来补答 用积化和差公式2sin(a)sin(b)=cos(a-b)-cos(a+b)则2sin(x/2)*sin(x)=cos(x/2)-cos(3x/2)2sin(x/2)*sin(2x)=cos(3x/2)-cos(5x/2)2sin(x/2)*sin(3x)=cos(5x/2)-cos(7x/2)...2sin(x/2)*sin(nx)=cos((n-1/2)x)-cos((2n+1)x/2)上面所有式子相加得到左边=2(sinx/2)*∑sinkx=右边=(cosx/2)-cos(2n+1)*x/2) 展开全文阅读