很简单,主要对1/4*sin2x*sin4x进行化简：1/4*sin2x*2*sin2x*cos2x=2sin^2x*cos^2x*cos2x;
然后右式乘以cos^2x-sin^2x化为cos2x ,提取公因式,结果一目了然了
求证（cos^2x-sin^2x)(cos^4x+sin^4x）+1/4sin2xsin4x=cos2x
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