题目内容
先化简,再求值:当x=2,y=-1时,求
-
÷
的值.
xy2 |
x2-y2 |
x4y |
x4-y4 |
x2 |
x2+y2 |
分析:将除法转化为乘法,然后将分式因式分解,约分后再通分.
解答:解:原式=
-
•
=
-
=
=
=-
原式=-
=2.
xy2 |
x2-y2 |
x4y |
(x2-y2)•(x2+y2) |
x2+y2 |
x2 |
=
xy2 |
x2-y2 |
x2y |
x2-y2 |
=
xy2-x2y |
x2-y2 |
=
xy(y-x) |
(x-y)(x+y) |
=-
xy |
x+y |
原式=-
2×(-1) |
2+(-1) |
点评:本题考查了分式的化简求值,学会通分、约分及因式分解是解题的关键.
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