试题

题目:
(2009·成都)化简:1-
x+y
x-4y
÷
x2-y2
x2-9xy+9y2
=
2y
x-y
2y
x-y

答案
2y
x-y

解:1-
x+y
x-3y
÷
x2-y2
x2-6xy+9y2
=1-
x+y
x-3y
·
(x-3y)2
(x+y)(x-y)
=1-
x-3y
x-y
=
x-y-x+3y
x-y
=
2y
x-y
考点梳理
分式的混合运算.
把第二个分式的分子分母先因式分解,再把除法统一成乘法化简,最后算减法.
此题运算顺序:先除后减,用到了分解因式、约分、合并同类项等知识点.
计算题.
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