若m-n=4,mn=-1

来源：百度知道编辑：UC知道时间：2024/06/21 19:58:53

若m-n=4,mn=-1,求（-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)

（-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
=(-2mn-3mn-mn) + (2m+3n-2n+2m-m-4n)
=-6mn+3(m-n)
=6+12
=18

当然也可以先解方程，求出m n的值，再代入运算

先化简再代值。
（-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
=-2mn+2m+3n-3mn-2n+2m-m-4n-mn
=(-2mn-3mn-mn) + (2m+3n-2n+2m-m-4n)
=-6mn+3(m-n)
=6+12
=18

（-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
=(-2mn-3mn-mn) + (2m+3n-2n+2m-m-4n)
=-6mn+3(m-n)
=6+12
=18

=-2mn+2m+3m-3mn-2n+2n-m-4m-mn
=-2mn-3mn-mn+2m+3m-m-4m+2n-2n
=6mn
=6*5*(-1)
=-30

把括号拆开，合并同类项就出来了，然后把上面的数代入就算出来了。