[（x²+y²）-（x-y）²+2y（x-y）]÷4y
=（x²+y²-x²+2xy-y²+2xy-2y²）÷4y
=（4xy-2y²）÷4y
=x-

1

2

y
∵x-

1

2

y=1，
∴2x-y=2，
∴

4x

4x2−y2

-

1

2x+y

，
=

4x

(2x+y)(2x−y)

-

1

2x+y

=

4x−2x+y

(2x+y)(2x−y)

=

2x+y

(2x+y)(2x−y)

=

1

2x−y

=

1

2

．