题目

1X-1Y=3,求5X+XY-5YX-XY-Y的值.
2-XX-3=13-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=___

提问时间：2020-10-25

答案

∵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