若分式x y分之x-y中的x,y的值都变为-搜答案-大师作文网

很简单啊,xy都扩大两倍,那么xy/(x+y)就变成了4xy/2(x+y),把扩大了的这个数去除以原来的xy/(x+y),就是:[4xy/2(x+y)]/[xy/(x+y)]=[4xy/2(x+y)]

1/X+1/Y=2两边同乘以XY,得Y+X=2XY,于是,XY=（X+Y)/2(2X+3XY+2Y)/(X-XY+Y)=7楼上的刚好写反了.

1/x+1/y=2则(2x+3xy+2y)/(x-xy+y)分子分母同除以xy=(2/x+2/y+3)/(1/x+1/y-1)=(4+3)/(2-1)=7

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=

1/x-1/y=2001则(x-xy-y)/(x-y)=2002/2001

-12后有没有x

x-y=x/y两边同乘以y得xy-y^2=x移项xy-x=y^2即x(y-1)=y^2x=y^2/(y-1)

1、1/x-1/y=3(y-x)/xy=3y-x=3xyx-y=-3xy原式=[3(x-y)+xy]/[(x-y)-xy]=[3(-3xy)+xy]/[(-3xy)-xy]=-8xy/(-4xy)=2

xy/(x+y)变为3Xx3Y/(3X+3Y)=3XY/(X+Y)

等于原来分式值的三分之一

1/x-1/y=(y-x)/xy=1y-x=xy(3y-xy-3x)/(x-xy-y)=(3y-y+x-3x)/(x-y+x-y)(2y-2x)/(2x-2y)=-1

正确答案是C.若是3x+4y=0的话,那分式出的就没意义了,考虑问题不要太偏激!那要是你所说,所有的分式分子都为0的话,还不用计算了呢!所以说你那是特殊情况,比如说,我说四边形的四个角是直角,你判断他

(x+3y)/(x²+xy)+(y-x)/(xy+y²)=(x+3y)[x(x+y)]-(x-y)/[y(x+y)]=[(x+3y)y-x(x-y)]/[xy(x+y)]=(xy+

因为x=3y,所以原式=[（3y)²-3y·y+y²]分之[(3y)²+2·3y·y-3y²]=7y²分之12y²=7分之12

x²-3xy+2y²=(x-y)(x-2y)=0x-y≠0,所以x-2y=0x=2y原式=(4y-3y)/(2y-y)=y/y=1

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

1/x-1/y=3(y-x)/xy=3y-x=3xy分式的分母=x-2xy-y=(x-y)-2xy=-5xy分子=2x+3xy-2y=2(x-y)+3xy=-3xy所以原式=3/5

方法一：取特殊值x=1,y=2,代入即可.方法二：由y/x=2,得y=2x,代入要求的式子也行,但是注意运算要小心点.

2xy/x+y2x.2y/2x+2y=4xy/2*(x+y)=2xy/x+y不知道对不对

等式两边除以xy所以1/y-1/x=1