∵a=

1

2+ 3

，
∴a=2-

3

＜1，
∴原式=

(a−1)2

a−1

-

(a−1)2

a(a−1)

=a-1-

1−a

a(a−1)

=a-1+

1

a

=2-

3

-1+2+

3

=4-1
=3．