计算(2m+3n)^2(2m-3n)^2
问题描述：
计算(2m+3n)^2(2m-3n)^2
同上
答
(2m+3n)²(2m-3n)²
=[(2m+3n)(2m-3n)]²
=[(2m)²-(3n)²]²
=(4m²-9n²)²
=(4m²)²-2×4m²×9n²+(9n²)²
=16m^4-72m²n²+81n^4