问题描述： 证明sin(x+y)sin(x-y)=sinx-siny 1个回答 分类：数学 2014-10-29 问题解答： 我来补答 sin(x+y)sin(x-y) =-1/2(cos(x+y+x-y)—cos(x+y-x+y)) =-1/2(cos2x—cos2y) =-1/2(1-2（sinx）^2-1+2(siny）^2) =（sinx）^2-(siny）^2 展开全文阅读
