1\X-1\Y=3,求5X+XY-5Y\X-XY-Y的值.2-X\X-3=1\3-X  -2(2X^2-4XY)\(X-2Y)=已知a^m=2,a^n=3,则a^m+n=___,a^2n=___若X^2+MXY+81Y^2是一个完全平方式,则M=___

1 1/x-1/y=3 y-x=3xy
而5X+XY-5Y\X-XY-Y=(-5*3xy+xy)/(-3xy-xy)=7/2
2 2-X\X-3=1\3-X -2 没看懂什么意思 2-X\X-3=1\（3-X）-1
3 (2X^2-4XY)\(X-2Y)=2x
4 a^m+n=a^m*a^n=3*2=6
a^2n=a^n*a^n=3*3=9
5 X^2+MXY+81Y^2是一个完全平方式 只需根的判别式=0 M^2-4*81=0
M=正负18

∵1/X-1/Y=3
∴X-Y=-3XY
∵5X+XY-5Y/X-XY-Y=[5(X-Y)+XY]/[(X-Y)-XY]
∴[5(-3XY)+XY]/(-3XY-XY)
即 原式=(-15XY+XY)/(-4XY)
=14XY/4XY
=3.5
(2-X)/(X-3)=1/(3-X)-2
(2-X)/(X-3)=-1/(X-3)-2
(2-X)/(X-3)=[-1-2(X-3)]/(X-3)
(2-X)/(X-3)=[5-2X]/(X-3)
(2-X)/(X-3)-[5-2X]/(X-3)=0
(2-X-5+2X)/(X-3)=0
(X-3)/(X-3)=0
方程无解
(2X^2-4XY)\(X-2Y)
=2X(X-2Y)/(X-2Y) (X≠2Y )
=2X
已知a^m=2,a^n=3，则a^m+n=___,a^2n=___
a^m+n=a^m*a^n=2*3=6
a^2n=(a^n)^2=3^2=9
若X^2+MXY+81Y^2是一个完全平方式，则M=___
(X±9Y)^2=X^2±18XY+81Y^2
M=±18

1/X-1/Y=3
两边都乘XY得:Y-X=3XY
(5X+XY-5Y)/(X-XY-Y)=(-15XY+XY)/(-3XY-XY)=3.5
(2-X)/(X-3)=1/(3-X)-2
两边都乘以X-3得:2-X=-1-2(X-3)
得到X=3 但X-3=0即X=3为增根,方程无解
(2X^2-4XY)/(X-2Y)=2X(X-2Y)/(X-2Y)=2X (X≠2Y)
a^m+n=a^m*a^n=2*3=6
a^2n=(a^n)^2=3^2=9
(X±9Y)^2=X^2±18XY+81Y^2
M=±18

题明显出错了，5X+XY-5Y\X-XY-Y，其中xy项是不是可以消掉了？

1\X-1\Y=3,求5X+XY-5Y\X-XY-Y的值.
1/x-1/y=3
(y-x)/xy=3
y-x=3xy
x-y=-3xy
(5x+xy-5y)/(x-xy-y)
=[5(x-y)+xy][(x-y)-xy]
=(-15xy+xy)/(-3xy-xy)
=-14xy/(-4xy)
=7/2
2-X\X-3=1\3-X -2
2-x=-1-2(x-3)
2-x=-1-2x+6
x=3
经检验,x=3是方程的增根,原方程无解.
(2X^2-4XY)\(X-2Y)=2X(X-2Y)/(X-2Y)=2X
已知a^m=2,a^n=3,则a^m+n=_a^m*a^n=2*3=6__,a^2n=_(a^n)^2=3^2=9__
若X^2+MXY+81Y^2是一个完全平方式,则M=__-18或+18_
x^2+mxy+81y^2=(x+9y)^2或=(x-9y)^2
展开得m=18,-18