1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55+1/66

1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55+1/66
1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55+1/66

1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55+1/66
原式=2/(2×3)+2/(3×4)+2/(4×5)+2/(5×6)+……+2/(15×16)
=2(1/2-1/3+1/3-1/4+1/4-1/5+……+1/15-1/16)
=2×(1/2-1/16)
=7/32