4m²n²-(m²+n²-x²）²
=（2mn+m²+n²-x²)(2mn-m²-n²+x²)
=[(m+n)²-x²][-(m-n)²+x²]
=(m+n+x)(m+n-x)(x+m-n)(x-m+n)不知对不对我认了对滴