=1+1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+1/(5×6) =1+[1-(1/2)]+[(1/2)-(1/3)]+[(1/3)-(1/4)]+[(1/4)-(1/5)]+[(15)-(1/6)] =1+1-(1/6) =2-(1/6) =11/6.
原式=1+(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6) =1+1-1/6 =1+5/6 =1又5/6
答：先求得an=1/n 由等差数列前N项和公式得Sn=2（a1+an)/n =(2+2n)/（n的平方）详情>>
答：详情>>
