分式题目几道，各位高手救我！

来源：百度知道 编辑：UC知道 时间：2024/05/15 05:52:26
1、若x^2-3xy-4y^2=0(y≠0)，则(x-2y)/(x-y)=几？
2、计算：[x-y+(4xy)/(x-y)][x+y-(4xy/x+y)]
3、已知(1/x)+(1/y)=3，x+y=6,则xy=几？
上述几题全要具体步骤！！谢谢各位高手~~

1.x^2-3xy-4y^2=0
即(x-4y) (x+y)=0则x=4y或x=-y,
分别代入分式消x再约y.
2. [x-y+(4xy)/(x-y)]
=[(x-y)^2+4xy]/(x-y)
=[x^2-2xy+y^2+4xy]/(x-y)
=[x^2+2xy+y^2]/(x-y)
=[(x+y)^2]/(x-y)
同理右边=[(x-y)^2]/(x+y)
原式=[(x+y)(x-y)]^2/(x+y)(x-y)
=(x+y) (x-y)
=x^2-y^2
3.(1/x)+(1/y)=3等号左右同乘xy得y+x=3xy,因为x+y=6所以xy=2.