Question

已知m-n=3,求代数式m2-n2+2m-8n-4的值

Answer 1

这类题如果是选择或者填空~~可以取巧一下~~~令m=3，n=0代入~~~既然这么出了~后面求解的代数式肯定符合所有m-n=3的任意mn的取值~这样怎么简单怎么来呗~

Answer 2

m2-n2+2m-8n-4
=(m-n)(m+n)+2m-8n-4
=3(m+n)+2m-8n-4
=3m+3n+2m-8n-4

=5m-5n-4
=5(m-n)-4
=5*3-4
=11

希望对你有所帮助
如有问题，可以追问。
谢谢采纳

Answer 3

除了整体代入外，还有一种解题思路，化两个字母为一个字母。
m=n+3
原式=(n+3)^2-n^2+2(n+3)-8n-4
=n^2+6n+9-n^2+2n+6-8n-4
=11.

Answer 4

m2-n2+2m-8n-4
=(m-n)(m+n)+2m-8n-4
=3m+3n+2m-8n-4
=5m-5n-4
=5(m-n)-4
=15-4
=11