题目内容
化简求值：(1+
)•
，其中x-3y=0，且y≠0．
| y2 |
| x2-y2 |
| x-y |
| x |
原式=(
+
)•
=
•
=
•
=
．
由x-3y=0，得x=3y，
∴原式=
=
=
．
| x2-y2 |
| x2-y2 |
| y2 |
| x2-y2 |
| x-y |
| x |
=
| x2 |
| x2-y2 |
| x-y |
| x |
=
| x2 |
| (x+y)(x-y) |
| x-y |
| x |
=
| x |
| x+y |
由x-3y=0，得x=3y，
∴原式=
| 3y |
| 3y+y |
| 3y |
| 4y |
| 3 |
| 4 |
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，y=-1）．