(7m²-4mn-n²)-(3m²-mn+2n²)求解
问题描述：
(7m²-4mn-n²)-(3m²-mn+2n²)求解
答
(7m²-4mn-n²)-(3m²-mn+2n²)
=(7m²-4mn-n²)-3m²+mn-2n²
=4m²-3mn-3n²