1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=
问题描述:
1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=
答
1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1+1-1/2+1/2-1/3+……+1/9-1/10
=1+1-1/10
=19/10