已知x-y等于xy,则x分之一-y分之一等于多少

1/x-1/y=3等号左边通分,得(y-x)/(xy)=3故x-y=-3xy代入分式[2x+3xy-2y]/[x-2xy-y]=[2(x-y)+3xy]/[(x-y)-2xy]=(-6xy+3xy)/

解题思路：本题目关键1/x+1/y=1/3变型，得到x-y和xy的关系式。解题过程：

1/x-1/y=10(y-x)/xy=10y-x=10xy所以原式=[3(y-x)-6xy]/[(y-x)-2xy]=(30xy-6xy)/(10xy-2xy)=24xy/8xy=3

由　1/X-1/Y=5,两边同乘　XY,得出Y-X=5XY,那么　　分子　-X+XY+Y=6XY分母　2X+7XY-2Y=7XY-2(Y-X)=-3XY　　得此分式的值为－再问：还有一题x+x分之一=

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

(1/x+1/y)^2=251/x^2+2/xy+1/y^2=251/x^2+1/y^2=27(1/x^2+1/y^2)^2=7291/x^4+1/y^4+2/x^2y^2=7291/x^4+1/y^

X分之一减y分之一=(y-x)/xy=3y-x=3xy2X一14Xy一2y除以x一2xy一y=[2(x-y)-14xy]/[(x-y)-2xy]=[-6xy-14xy]/[-3xy-2xy]=4

1／X－1／Y＝3（Y－X）／XY＝3Y－X＝3XY〔－2（Y－X）＋3XY〕／〔－（Y－X）－2XY〕＝（－6XY＋3XY）／（－3XY－2XY）＝－3XY／－5XY＝3／5

14

x分之1-y分之1=4(xy)分之(y-x)=4y-x=4xyx-y=-4xy(x-2xy-y)分之(2x+xy-2y)=[(x-y)-2xy]分之[2(x-y)+xy]=(-4xy-2xy)分之(-

1/X-1/Y=4Y-X=4XY(2X+XY-2Y)/(X-2XY-Y)=[2(X-Y)+XY]/[(X-Y)-2XY]=7/6

X分之一减去Y分之一等于1(y-x)/(xy)=1y-x=xyx-y=-xyx-2xy-y分之2x+3xy-2y=[2(x-y)+3xy]/[(x-y)-2xy]=(-2xy+3xy)/(-xy-2x

答案是4.先把已知条件通分,化简,得到X-Y=-3XY,在把它带入所求式子,为：-5XY分之-20XY.

[2x+14xy-2y]/[3x-2xy-3y]=(2/y+14-2/x)/(3/y-2-3/x)分子分母同时除以xy=[-2(1/x-1/y)+14]/[-3(1/x-1/y)-2]=(-6+14)

1/x-1/y=3(y-x)/xy=3y-x=3xyx-y=-3xyx-2xy-y分之2x-14xy-2y=[2(x-y)-14xy]/[(x-y)-2xy]=(-20xy)/(-5xy)=4

1/x-1/y=3通分(y-x)/xy=3y-x=3xyx-y=-3xy原式=[(x-y)-xy]÷[5(x-t)+xy]=(-3xy-xy)/(-15xy+xy)=-4xy/(-14xy)=2/7

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

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)=

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

再问：为什么xy分之等于5y减x再问：为什么xy分之y减x等于5再答：通分，分式相加减啊再问：怎么通分的，概念是什么再答：第一步：求出所要通分的几个分式分母的最小公倍数。第二步：运用分式的基本性质，把