问题标题：
【tan(x+y)tan(x-y)=sin^2x-sin^2y/cos^2x-sin^2y顺便问一下.tan,sin,cos是什么意思?】
问题描述：
tan(x+y)tan(x-y)=sin^2x-sin^2y/cos^2x-sin^2y顺便问一下.tan,sin,cos是什么意思?
潘荣江回答：
tan,正切；sin,正弦；cos,余弦tan(x+y)tan(x-y)=sin(x+y)/cos(x+y)*sin(x-y)/cos(x-y)=sin(x+y)sin(x-y)/[cos(x+y)cos(x-y)]=(sinxcosy+cosxsiny)(sinxcosy-cosxsiny)/[(cosxcosy-sinxsiny)(cosxcosy+sinxsiny...
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