120/(x-y) 120/(x y)=160/y 怎样化简成x＝2y和x＝-1/2y 急！急！在线等！

千问 · 2011-9-26 09:45:12

120/(x-y)120/(xy)=160/y3/(x-y)3/(xy)=4/y6x/(x^2-y^2)=4/y4x^2-4y^2=6xy2^2-3xy-2y^2=0（2xy)(x-2y)=0所以x＝2y或x＝-1/2y追问4x2－4y2＝6xy是怎么来的？我会提高为你提高悬赏的

千问 · 2011-9-26 09:45:12

方程两边乘以(x^2-y^2)y就是去分母啊...

千问 · 2011-9-26 09:45:12

120/(x-y)120/(xy)=160/y3/(x-y)3/(xy)=4/y左边通分6x/(x^2-y^2)=4/y3xy=2x^2-2y^2就是2x^2-3xy-2y^2=0因式分解得（x-2y)(2xy)=0x=2y或x=-1/2y望采纳O(∩_∩)O谢谢追问3xy＝2x2－2y2怎么来的？我已经提高了悬赏！

千问 · 2011-9-26 09:45:12

2边同时乘以y(xy)(x-y)120y(xy)120(x-y)=160(x-y)(xy)240xy=160(x-y)除以80,3xy=2x-2y2(x-3/2xy)-2y=02(x-3/2xy9/16y-9/16y)-2y=02(x-3/4y)-9/8y-2y=02(x-3/4y)=25/8y(x-3/4y)=25/16yx-3/4y=±5/4y所以x=1/2y或x=-2y