计算. 1/2+1/6+1/20+1/30+1/42+1/56+1/72.

问题描述:

计算.

1
2
+
1
6
+
1
20
+
1
30
+
1
42
+
1
56
+
1
72

1
2
+
1
6
+
1
20
+
1
30
+
1
42
+
1
56
+
1
72

=1-
1
2
+(
1
2
-
1
3
)+(
1
4
-
1
5
)+(
1
5
-
1
6
)+(
1
6
-
1
7
)+(
1
7
-
1
8
)+(
1
8
-
1
9

=1-
1
3
+
1
4
-
1
9

=
2
3
-
1
9
+
1
4

=
1
3
+
1
4

=
7
12