1/20+1/30+1/42+…+1/132.
问题描述:
+1 20
+1 30
+…+1 42
. 1 132
答
+1 20
+1 30
+…+1 42
,1 132
=(
−1 4
)+(1 5
−1 5
)+(1 6
−1 6
)+…+1 7
−1 11
,1 12
=
−1 4
,1 12
=
.1 6