2/3+2/9+2/27+2/81+2/243.

问题描述:

2
3
+
2
9
+
2
27
+
2
81
+
2
243

2
3
+
2
9
+
2
27
+
2
81
+
2
243

=1-
1
3
+
1
3
-
1
9
+
1
9
-
1
27
+
1
27
-
1
81
+
1
81
-
1
243

=1-
1
243

=
242
243