已知m-n=2,mn=1,求多项式(2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)的值
问题描述：
已知m-n=2,mn=1,求多项式(2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)的值
答
(2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
先去括号
=2mn+2m+3n-3mn-2n+2m-m-4n-mn
合并同类项
=-2mn+3m-3n
=-2mn+3(m-n)
把m-n=2,mn=1代入
=-2*1+3*2
=-2+6
=4