General term and summation of sequence Given that the first n terms and Sn of sequence {an} satisfy an + 2snsn-1 = 0, (n is greater than or equal to 2), A1 = 1 / 2, find an

An=Sn-Sn-1
So the original formula = sn-sn-1 + 2snsn-1 = 0
Divide by 2snsn-1 at the same time
1/Sn-1/Sn-1=2
So 1 / Sn is an arithmetic sequence
1/S1=2
1/Sn=2+（n-1）*2=2n
So Sn = 1 / 2n
Then sn-sn-1 = an is used to calculate an
An=1/2n-1/2n-1
It should be

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