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
答
+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