(1)原式=(
x-1
x-1 +
1
x-1 )•
(x-1)(x+1)
x
=
x
x-1 •
(x-1)(x+1)
x
=x+1;
当x=2时,原式=2+1=3;
(2)原式=
1
2 a+1-a+
(a-1)(a+1)
(a-1)
=
1
2 a+1-a+a+1
=
1
2 a+2;
当a=2时,原式=
1
2 ×2+2=3;
(3)原式= (
x-1
x+1 +
1
x 2 -1 )•( x 2 -1)
= (
x-1
x+1 +
1
x 2 -1 )•(x-1)(x+1)
=
x-1
x+1 •(x-1)(x+1)+
1
(x-1)(x+1) (x-1)(x+1)
=(x-1) 2+1
=x 2-2x+1+1
=x 2-2x+2;
当x=2时,原式=2 2-2×2+2
=4-4+2
=2;
(4)原式=
a 2 -2a+1
a •
a(a+1)
(1-a)(1+a)
=
(a-1 ) 2
a •
a(a+1)
(1-a)(1+a)
=1-a;
当x=2时,原式=1-2=-1;
(5)原式=
a-b
a+2b •
(a+2b ) 2
(a-b)(a+b) -1
=
a+2b
a+b -1
=
a+2b-a-b
a+b
=
b
a+b ;
当a=1,b=2时,原式=
2
1+2 =
2
3 .