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：2020-11-11

答案

1X-1Y=3,求5X+XY-5YX-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-XX-3=13-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