Question

已知

1

x

-

1

y

=3，则

5x+xy-5y

x-xy-y

的值为______．

Answer 1

∵

1

x

-

1

y

=

y-x

xy

=3，
∴y-x=3xy，即x-y=-3xy，
则

5x+xy-5y

x-xy-y

=

5(x-y)+xy

(x-y)-xy

=

-15xy+xy

-3xy-xy

=

-14xy

-4xy

=

7

2

．
故答案为：

7

2