方法：
1、从已知条件得：X+Y=3XY，
2、把(X+Y)用3XY代入，
3、整理，并把XY约去。
已知1\/x+1\/y=3,求(3x-5xy+3y)\/(x-2xy+y)
1\/x+1\/y=3 去分母得 x+y=3xy (3x-5xy+3y)\/(x-2xy+y)=[3(x+y)-5xy]\/(x+y-2xy)=(9xy-5xy)\/(3xy-2xy)=4xy\/xy=4
有几道数学题:当1\/x+1\/2y=3时,求分式(2x+3xy+4y)\/(x-3xy+2y)的值
1\/x+1\/2y=3 两边乘以2xy得 x+2y=6xy 所以2x+3xy+4y=15xy x-3xy+2y=3xy 所以(2x+3xy+4y)\/（x-3xy+2y）=5 呵呵 给分吧
2.已知1\/x+1\/y=3,则(3x+xy+3y)\/(x-xy+y)=( ).
因为 1\/x+1\/y=3,所以 x + y = 3xy,代入:（3x+xy+3y）\/(x-xy+y)=[3( x+y)+xy]\/(x+y-xy)=4xy\/(2xy)=2
已知1\/x+1\/y=3,求(x+xy+y)\/(2x-3xy+2y) 的值
答：1\/x+1\/y=3 (x+xy+y) \/(2x-3xy+2y) 分子分母同时除以xy得：=(1\/y+1+1\/x) \/(2\/y-3+2\/x)=(3+1) \/(2*3-3)=4\/3
1\/X +1\/Y=3,则(2X+3XY-2Y)\/(X-2XY-Y)=多少?
解：由已知1\/X + 1\/Y = 3 => (X + Y)\/(XY)= 3 => X + Y = 3XY => XY = (X + Y)\/3，所以原式 = (2X + 3XY –2Y)\/(X –2XY –Y)= (2X + X + Y –2Y)\/[X –2*(X + Y)\/3 –Y]= (3X –Y)\/(X\/3 –5Y\/3)= 3(3X –Y)(X –5Y)，（无法再...
若1\/x-1\/y=3,则分式(2x+3xy-2y)\/(3x-2xy-3y)=
1\/x-1\/y=3 (y-x)\/xy=3 y-x=3xy (2x+3xy-2y)\/(3x-2xy-3y)=(3xy-6xy)\/(-2xy-9xy)=3\/11
已知1\/x+1\/y=5,求(2x-3xy+2y)\/(x+2xy+y)的值
1\/x+1\/y=5 两边都乘以xy y+x=5xy 所以：（2x-3xy+2y)\/(x+2xy+y)=[2(x+y)-3xy]\/[(x+y)+2xy]=(10xy-3xy)\/(5xy+2xy)=7xy\/7xy =1
已知1\/x+1\/y=4,求(x+y+2xy)\/(2x-3xy+2y)的值
由1\/x+1\/y=4,得,x+y=4xy,所以（x+y+2xy）\/（2x-3xy+2y）=（4xy+2xy）\/（8xy-3xy）=6\/5
已知1\/x-1\/y=5,求分式2x+3xy-2y\/x-2xy-y的值
有类似的题目，自己好好想想 已知1\/x-1\/y=3,求分式2x+3xy-2y\/x-2xy-y的值 根据条件可得y-x=3xy(方程1\/x-1\/y=3两边同乘xy)所以分式的分子可以化简为2x+3xy-2y =2（x-y）+3xy =-6xy+3xy =-3xy 分式的分母x-2xy-y =-3xy-2xy=-5xy 所以答案为3\/5(五分之三)...
若1\/x-1\/y=3,试求(2x-3xy-2y)\/(x-2xy-y)的值。
y)=(x - xy - y + x - 2xy - y)\/(x - 2xy - y)=(x - xy - y)\/(x - 2xy - y)+1 =(-3xy - xy)\/(-3xy - 2xy)+1 =(-4)\/(-5)+1 =9\/5 另外，以后要是遇到类似问题，一时想不起简便方法，可以直接代数字，我以前就这么干 比如这题，设x=1，y=-1\/2，答案...
