若m-n=4,mn=-1求(9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)

来源：学生作业帮助网编辑：作业帮时间：2024/04/29 02:26:10

若m-n=4,mn=-1求(9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
若m-n=4,mn=-1求(9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)

若m-n=4,mn=-1求(9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
先合并同类项,得3(m-n)-6mn+9,代入已知数据,有结果27

(9-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)
=9-2mn+2m+3n-3mn-2n+2m-m-4n-mn
=9-6mn+3m-3n
=9-6mn+3(m-n)
=9-6*(-1)+3*4
=9+6+12
=27

先去括号。
=9-2mn+2m+3n-3mn-2n+2m-m-4n-mn
=9-6mn+3m-3n
=9+6+3(m-n)
这样你应该知道答案了吧

解:
原式=9-2mn+2m+3n-3mn-2n+2m-m-4n-mn
=9-2mn-3mn-mn+2m+2m-m+3n-2n-4n
=9-6mn+3m-3n
因为m-n=4,mn=-1
所以3*(m-n)=12
所以
=9-6*(-1)+3*4
这里运用到合并同类项,这一楼说对了,另外还有用到整体代入法,这种方法是很重要的
=9+6+12
=27

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