Arithmetic sequence {an} A1 = 2, d = 2, find the first n terms and Sn, and find the first n terms and TN leading to formula {1 / Sn}
Sn=nA1+(1/2)n(n-1)d=2n+n(n-1)=n(n+1)
1/Sn=1/[n(n+1)]=[(n+1)-n]/[n(n+1)]=1/n-1/(n+1)
Tn=1/S1+1/S2+…… +1/Sn
=(1/1-1/2)+(1/2-1/3)+…… +(1/n-1/(n+1))
=1-1/(n+1)
=n/(n+1)
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