证明sin(x+y)sin(x-y)=sinx-siny

发布时间：2021-02-19 20:53:58

证明sin(x+y)sin(x-y)=sinx-siny

网友回答

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
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