求证:tan(x+y)+tan(x-y)=sin2xcos

问题描述:

求证:tan(x+y)+tan(x-y)=
sin2x
cos
1个回答 分类:数学 2014-10-21

问题解答:

我来补答
证明:左=
sin(x+y)
cos(x+y)+
sin(x−y)
cos(x−y)
=
sin[(x+y)+(x−y)]
cos2x•cos2y−sin2x•sin2y
=
sin2x
cos2x−(cos2x+sin2x)sin2y
=
sin2x
cos2x−sin2y=右.
 
 
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