(1)
1
42 =
1
6×7 =
1
6 -
1
7 ,
故答案是:
1
6 -
1
7 ;
(2)
1
m(m+1) =
1
m -
1
m+1 ;
(3)原式=
1
x-3 -
1
x-2 -2×
1
2 (
1
x-3 -
1
x-1 )+
1
x-2 -
1
x-1
=
1
x-3 -
1
x-2 -
1
x-3 +
1
x-1 +
1
x-2 -
1
x-1
=0.
(1)
1
42 =
1
6×7 =
1
6 -
1
7 ,
故答案是:
1
6 -
1
7 ;
(2)
1
m(m+1) =
1
m -
1
m+1 ;
(3)原式=
1
x-3 -
1
x-2 -2×
1
2 (
1
x-3 -
1
x-1 )+
1
x-2 -
1
x-1
=
1
x-3 -
1
x-2 -
1
x-3 +
1
x-1 +
1
x-2 -
1
x-1
=0.