（

1

x-y

-

1

x+y

）÷

xy2

x2-y2

，
=（

1

x-y

-

1

x+y

）•

(x-y)(x+y)

xy2

，
=

1

x-y

•

(x-y)(x+y)

xy2

-

1

x+y

•

(x-y)(x+y)

xy2

，
=

x+y

xy2

-

x-y

xy2

，
=

2y

xy2

，
=

2

xy

，
当x=

2

+1，y=

2

-1时，原式=

2

( 2 +1)( 2 -1)

=2．