觀察:計(jì)算:
1
1×2
+
1
2×3
=(1-
1
2
)+(
1
2
-
1
3
)=1-
1
3
=
2
3
1
1×2
+
1
2×3
+
1
3×4
=(1-
1
2
)+(
1
2
-
1
3
)+(
1
3
-
1
4
)=1-
1
4
=
3
4

計(jì)算:
1
1×2
+
1
2×3
+
1
3×4
+…+
1
n(n+1)
=______
1
1×2
+
1
2×3
+
1
3×4
+…+
1
n(n+1)
,
=1-
1
2
+
1
2
-
1
3
+
1
3
-
1
4
+…+
1
n
-
1
n+1
,
=1-
1
n+1

=
n
n+1
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