已知y分之x等于3,那么x y分之x-y的值为

1/x-1/y=2y-x=2xyx-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=[-6xy+7xy]/[-4xy-3xy]=xy/[

(y-x)/xy=3求（2x+3xy-2y)/(x-2xy-y)?(y-x)/xy=3-->1/x-1/y=3-->y-x=3xy（2x+3xy-2y)/(x-2xy-y)=(x-y)/(-5xy)=

xy分之x加y等于2∴x+y=2xy3x减5xy加3y分之负x加3xy减y=[-(x+y)+3xy]/[3(x+y)-5xy]=(-2xy+3xy)/(6xy-5xy)=xy/(xy)=1

答：1/x+1/y=3(x-2xy+y)/(2x+xy+2y)分子分母同除以xy得：=(1/y-2+1/x)/(2/y+1+2/x)=(3-2)/(3*2+1)=1/7

x²-5xy+6y²=0,(x-3y)(x-2y)=0x=3y或x=2y(1)当x=3yx+y分之x-y=(3y-y)/(3y+y)=1/2(2)当x=2yx+y分之x-y=(2y

xy=6/(x+y)xy(x+y)=6,已知x和y是整数,则xy和(x+y)也是整数,而6=2*3=1*6当xy=3时,x+y=2,无整数解当xy=1时,x+y=6,无整数解当xy=6时,x+y=1,

xy/(x+y)=2∴xy=2(x+y)(3xy-x-y)/(3x-5xy+3y)=[6(x+y)-x-y]/[3x+3y-10(x+y)]=5(x+y)/[-7(x+y)]=-5/7

1/X-1/Y＝5（Y-X）/XY＝5Y-X＝5XY（3x+7xy-3y）/（2x-3xy-2y）＝[3（X-Y）+7XY]/[2（X-Y）-3XY]＝[-3（Y-X）+7XY]/[-2（Y-X）-3

解析：

因为1/x-1/y=3所以方程左边先通分得y/xy-x/xy=3即（y-x）/xy=3所以得y-x=3xy（这一步很关键,一会要用整体代入法)要求的分数的分子：x+xy-y=xy-3xy=-2xy(因

2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0

1/x-1/y=5通分(y-x)/xy=5y-x=5xyx-y=-5xy原式=[3(x-y)+5xy]/[(x-y)-3xy]=(-15xy+5xy)/(-5xy-3xy)=-10xy/(-8xy)=

1/x-1/y=3y-x=3xyx-y=-3xy(5x-xy-5y)/(x-xy-y)=(-15xy-xy)/(-3xy-xy)=4

x分之1减y分之1等于31/x-1/y=3(y-x)/xy=3y-x=3xy所以x-xy-y分之5x-xy-5y=（-3xy-xy）分之(-15xy-xy)=-4分之（-16）=4

已知xy/(x+y)=2,求:(3x-5xy+3y)/(-x+3xy-y)xy/(x+y)=2得：xy=2(x+y)(3x-5xy+3y)/(-x+3xy-y)=(3x-9xy+3y+4xy)/(-x

y-x=3xyx-y=-3xyx-2xy-y=-5xy2x+3xy-2y=2(x+y)+3xy=-6xy+3xy=-3xy分式x-2xy-y分之2x+3xy-2y=5/3

设x+y=axy=b,则b/a=3b=3a所以-X+3XY-Y分之2X-3XY+2Y可以写成(2a-3b)/(3b-a)=-7/8

xy分之【x加y】等于2分之一xy=2(x+y)【xy加x加y】分之xy=2(x+y)/[2(x+y)+x+y]=2(x+y)/[3(x+y)]=2/3

(x+y)/(x-y)=3/2[(x/y)+1]/[(x/y)-1]=3/23(x/y)-3=2(x/y)+2x/y=5y/x=1/5(x^2+y^2)/xy=x/y+y/x=5+1/5=26/5

x^2-4xy+3y^2=0(x-y)(x-3y)=0x=y或x=3y当x=y时(x-y)/(x+y)=(y-y)/(y+y)=0/2y=0当x=3y时(x-y)/(x+y)=(3y-y)/(3y+y