Question

....1、已知：X分之1减去Y分之1=3,则X-XY-Y分之3X+XY-3Y=（ ）2.若将分式X+Y分之X的平方减去

Answer 1

1、

1/x-1/y=3

(y-x)/xy=3

y-x=3xy

x-y=-3xy

原式=[3(x-y)+xy]/[(x-y)-xy]

=[3(-3xy)+xy]/[(-3xy)-xy]

=-8xy/(-4xy)

=2

2、

即=[(2x)²-(2y)²]/(2x+2y)

=(4x²-4y²)/(2x+2y)

=4(x²-y²)/[2(x+y)]

=2(x²-y²)/(x+y)

所以分尸的值是快来的2倍