当x=-1,y=2时,求分式3x-2y分之2x 3y值-搜答案-智慧作业帮

(xy+2y)-(x+2)/x^2-4=【y(x+2)-(x+2)】/(x+2)(x-2)=(y-1)/(x-2)=(7-1)/(3-2)=6

1.因为x+1/x=4,所以x≠0,所以把式子x^2/(x^4+x^2+1)的分子分母同除以x^2,得x^2/(x^4+x^2+1)=1/(x^2+1+1/x^2)=1/[(x+1/x)^2-2*x*

x^3-x^2-xy^2+y^3/-x^4+2x^2y^2-y^4=[(x^3+y^3)-xy(x+y)]/[-(x^2-y^2)^2]=[(x+y)(x^2-xy+y^2)-xy(x+y)]/[-(

x/y=3=>x=3y原式=(9y²+2*3y*y-3y²)/(9y²-3y*y+y²)=12/7再问：能不能先化简，后代入？再答：可以是可以，x²+

因为你的题目未表达清楚,所以按两种情况考虑解法1：当x=3,y=7时：(xy+2y)-[(x²-4)/(x-2)]=y(x+2)-(x+2)(x-2)/(x-2)=y(x+2)-(x+2)=

当x=-1时,分式无意义分母为03(-1)-b=0b=-3当x=4时,分式的值为0分子为02*4-a=0a=8

根据题意解得N=3.,M=-3(2M+N)/(M-N)=1/2

∵当x=-1是,分式无意义∴当x=-1时,3x+b=0即3*(-1)+b=0,则b=3又∵当x=4时,分式的值为0∴当x=4时,2x-a=0且3x+b≠0即2*4-a=0且3*4+3≠0则a=8∴代数

由题意得3*3-n≠0;3+m=01*3-n=0解得n=3;m=-3(2m+n)/(m-n)=(-3)/(-6)=1/2

把X=2,Y=2代入（ax+by）/(ax-by)=5,得到a=1.5b,把X=1,Y=-1代入（ax+by）/(ax-by)=1/5,得到的也是a=1.5b,所以,a,b的值在这里是求不出的.

不正确当x不等于4时原式=2/(x^2+4x)当x=4时原式分母=0,分式无意义.

x=0原式为0x=-1原式为-2x=1原式为2

1/x-1/y=5y-x=5xy(3x+5xy-3y)÷(x-3xy-y)=(-15xy+5xy)/(-5xy-3xy)=-10xy/(-8xy)=5/4

x=-1无意义,则：3*(-1)+b=0x=4分式=0,则：2*(4)-a=0所以：b=3,a=8;

C

1/x-1/y=2时(y-x)/xy=2y-x=2xy2x+3xy-2y/x-2xy-y=[3xy-2(y-x)]/[-2xy-(y-x)]=-xy/-4xy=1/4

原式=[(-2y)/(x^2)]/[1/(x^5y^2)]=-2x^3y^3=-2(xy)^3=-2(1/4*8)^3=-2*2^3=-16

原式分子分母同除以y²原式=[(xy+y²)/y²]/[(x²-xy)/y²]=[(x/y)+1]/[(x/y)²-(x/y)]=(3/4+

分式(xy+y^2)/(x^2-xy)=(x/y+1)/[(x/y)^2-x/y](分子分母同时除以y^2)=(3/4+1)/(9/16-3/4)(代值)=(7/4)/(-3/16)=-28/3

分式2x-1分之x-3,当x=3_时,分式值为零；当x=2分之1时,分式没有意义.