这个题可以用平方差公式:
4(m+n)²-9(m-n)²
=[2(m+n)]²-[3(m-n)]²
=[2(m+n)+3(m-n)][2(m+n)-3(m-n)]
=(2m+2n+3m-3n)(2m+2n-3m+3n)
=(5m-n)(5n-m)
=4(m²+2mn+n²)-9(m²-2mn+n²)
=4m²-9m²+8mn+18mn+4n²-9n²
=-5m²+26mn-5n²
原式=[2(m+n)]^2-[3(m-n)]^2
=[2(m+n)+3(m-n)]*[2(m+n)-3(m-n)]
=(5m-n)*(5n-m)
[2(m+n)+3(m-n)][2(m+n)-3(m-n)]