赞 魔高一丈ye 幼苗
共回答了21个问题采纳率：90.5% 举报
an=(n+1)/[n²(n+2)²]
=(1/4)(4n+4)/[n²(n+2)²]
=(1/4)[(n+2)²-n²]/[n²(n+2)²]
=(1/4)[1/n²- 1/(n+2)²]
Sn=a1+a2+...+an
=(1/4)[1/1²-1/3²+1/2²-1/4²+...+1/n²-1/(n+2)²]
=(1/4)[(1/1²+1/2²+...+1/n²)-(1/3²+1/4²+...+1/(n+2)²)]
=(1/4)[1/1²+1/2²-1/(n+1)²-1/(n+2)²]
=5/16 -1/[4(n+1)²] -1/[4(n+2)²]
=(1/4)(4n+4)/[n²(n+2)²]
=(1/4)[(n+2)²-n²]/[n²(n+2)²]
=(1/4)[1/n²- 1/(n+2)²]
Sn=a1+a2+...+an
=(1/4)[1/1²-1/3²+1/2²-1/4²+...+1/n²-1/(n+2)²]
=(1/4)[(1/1²+1/2²+...+1/n²)-(1/3²+1/4²+...+1/(n+2)²)]
=(1/4)[1/1²+1/2²-1/(n+1)²-1/(n+2)²]
=5/16 -1/[4(n+1)²] -1/[4(n+2)²]
1年前
10
可能相似的问题
-
已知数列{an}中,a1a2a3.an=n2+n,求通项公式an
1年前1个回答
-
已知数列{an}中,a1a2a3.an=n2+n,求通项公式an
1年前1个回答
-
已知数列{an}满足a1+a2+…+an=n2（n∈N+）．
1年前1个回答
-
1年前4个回答
你能帮帮他们吗
精彩回答