解9(m+n)²-4(m-n)²=[3(m+n)]²-[2(m-n)]²=[3(m+n)-2(m-n)][3(m+n)+2(m-n)]=(3m+3n-2m+2n)(3m+3n+2m-2n)=(m+5n)(5m+n)
9(m+n)²-4（m-n）²=9m²+9n²+18mn-(4m²+4n²-8mn)=5m²+5n²+26mn
