题目内容
先化简，再求值：（
-
）÷
，其中m=-3，n=5．
| 1 |
| m |
| 1 |
| n |
| m2-2mn+n2 |
| mn |
（
-
）÷
，
=
÷
=
×
=
×
=
将m=-3，n=5代入原式得：
原式=
=
=
．
| 1 |
| m |
| 1 |
| n |
| m2-2mn+n2 |
| mn |
=
| n-m |
| mn |
| (m-n)2 |
| mn |
=
| n-m |
| mn |
| mn |
| (m-n)2 |
=
| n-m |
| mn |
| mn |
| (n-m)2 |
=
| 1 |
| n-m |
将m=-3，n=5代入原式得：
原式=
| 1 |
| n-m |
| 1 |
| 5-(-3) |
| 1 |
| 8 |
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