[(2m-3m)的平方-(3m-n)的平方]÷(m+2n)
=[(2m-3n)+(3m-n)][(2m-3n)-(3m-n)]÷(m+2n)
=(5m-4n)(-m-2n)÷(m+2n)
=4n-5m你确定对么[(2m-3n)的平方-(3m-n)的平方]÷(m+2n)=[(2m-3n)+(3m-n)][(2m-3n)-(3m-n)]÷(m+2n)=(5m-4n)(-m-2n)÷(m+2n)=4n-5m