数列{an}得通项公式为an=1/(4n-3)(4n+1)求sn

问题描述:

数列{an}得通项公式为an=1/(4n-3)(4n+1)求sn

An=1/(4n-3)(4n+1)=[1/(4n-3)-1/(4n+1)]/4
Sn=[1-1/5+1/5-1/9+...+1/(4n-7)-1/(4n-3)+1/(4n-3)-1/(4n+1)]/4
=[1-1/(4n+1)]/4
=n/(4n+1)