问题标题：
【求证:sin^2/(sin-cos)-(sin+cos)/(tan^2-1)=sin+cos】
问题描述：
求证:sin^2/(sin-cos)-(sin+cos)/(tan^2-1)=sin+cos
刘清才回答：
sin^2/(sin-cos)-(sin+cos)/(tan^2-1)
=sin^2/(sin-cos)-(sin+cos)/[(sin^2/cos^2)-1]
=sin^2/(sin-cos)-(sin+cos)cos^2/(sin^2-cos^2)
=sin^2/(sin-cos)-cos^2/(sin-cos)
(sin^2-cos^2)/(sin-cos)
=sin-cos
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