已知x y=3 求分式2x^2-3xy 5y^2 x^2 3xy-y^2

1/x+1/y=3∴x+y=3xy3x-2xy+3y/x+xy+y=[3(x+y)-2xy]/[(x+y)+xy]=(9xy-2xy)/(3xy+xy)=7/4

2x-3y=0所以y=2x/3代入(x^2+xy-y^2)/(2x^2+xy-y^2)得到[x^2+x*2x/3-(2x/3)^2]/[2x^2+x*2x/3-(2x/3)^2]=(x^2+2x^2/

此题做法不止一种,这里给你一个较简单方便的做法如果是填空题,直接把x换成4,y换成3代入即可算出正确答案

1）由1/x-1/y=5,得(y-x)/xy=5,所以y-x=5xy,即x-y=-5xy(3x+5xy-3y)/(x-3xy-y)=[3(x-y)+5xy]/[(x-y)-3xy]=(-15xy+5x

x-3y=0x=3yx*2-xy+y*2/x*2+xy+y*2=(9y^2-3y^2+y^2)/(9y^2+3y^2+y^2)=7y^2/13y^2=7/13

再问：化简：（1）【(a+2/a^2-2a）+(8/4-a^2)】除以a-2/a（2）x-3/x^2-1+1/1-x（3）【a-（2a-1/a）除以1-a^2/a^2+a】再答：嗯嗯~~等我一会

首先化简通分1/x+1/y=5得：（x+y)/xy=5即有x+y=5xy将要求的分式化简：3x+xy+3y/x-2xy+y=3x+3y+xy/x+y-2xy（根据加法交换律）=3（x+y)+xy/(x

即(3x-4y)(x+y)=03x=4y或x=-y若3x=4yy=3x/4则y²=9x²/16,xy=3x²/4原式=(3x²/4-3x²)/(9x&

x=-2y(2xy+y^2)/(x^2-xy)=(-4y^2+y^2)/(4y^2+2y^2)=-3y^2/(6y^2)=-1/2再问：我算出来也是-1/2，可答案说是-15/28

y/x-x/y=5(y²-x²)/(xy)=5/等式左边通分x²-y²=-5xy(3x²+xy-3y²)/(2x²-xy-2y&#

因为:1/x-1/y=3(y-x)/xy=3x-y=-3xy（1）又因为：(2x+3xy-2y)/(x-2xy-y)=[2（x-y）+3xy]/[(x-y)-2xy]代入（1）得：（-6xy+3xy）

1/x-1/y=3（y-x）/xy＝3y-x＝3xy（4x-5xy－4y）/（3x-2xy-3y）＝（4（x－y）-5xy）/（3（x－y）－2xy）＝(4*-3xy-5xy)/(3*-3xy－2xy

因为已知x/y=2,所以x=2y代入算式得：（4y*y-2y*y+3y*y）/(4y*y+2y*y+6y*y)化简原式=5/12

3X-4y=03x=4yx:y=4:3x=4ay=3a3x²-y²分之x²＋2xy=(16a^2+2x4ax3a)/(3x16a^2-9a^2)=40a^2/39a^2=

3/5再问：详细过程呢再答：y-x=3xyx-y=-3xy代入得：(-6xy+3xy)/(-3xy-2xy)=-3/-5=3/5

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

∵x-y/xy=3∴x-y=3xy2x+3xy-2y/x-2xy-y=[2(x-y)+3xy]/[(x-y)-2xy]=(6xy+3xy)/(3xy-2xy)=9xy/(xy)=9

y/x－x/y=3,通分得到（y方-x方)/xy=3,得到y方-x方=3xy,两边同乘以-1,得到x方-y方=xy.(2x方+3xy-2y方)/(x方-2xy-y方)=[2(x方-y方)+3xy]/(

（Y－X）÷（XY）＝3可变形为Y-X=3XY（2X＋3XY－2Y）÷（X－2XY－Y）=(2X-2Y+3XY）÷(X-Y-2XY)={2（x-y)+3xy}÷(X-Y-2XY)={2(3xy)+3x