早教吧作业答案频道 -->数学-->
设Sn是等差数列{an}的前n项和,若a1=2,S5/5-S3/3=2,则数列｛1/Sn}的前10项和T10=A10/11B8/9C11/12D32/33
题目详情
设Sn是等差数列{an}的前n项和,若a1=2,S5 / 5- S3 / 3=2,则数列｛1/Sn}的前10项和T10=
A10/11 B8/9 C11/12 D32/33
A10/11 B8/9 C11/12 D32/33
▼优质解答
答案和解析
S5 / 5- S3 / 3=a3-a2=d=2 an=2n
sn=(2n+2)*n/2=(n+1)*n
1/sn=1/[(n+1)*n]=1/n-1/(n+1)
T10=1-1/2+1/2-1/3+...+1/10-1/11=10/11
sn=(2n+2)*n/2=(n+1)*n
1/sn=1/[(n+1)*n]=1/n-1/(n+1)
T10=1-1/2+1/2-1/3+...+1/10-1/11=10/11
看了 设Sn是等差数列{an}的前...的网友还看了以下：