Question

2Sn=an+an,(an>0).求数列an的通项公式

Answer 1

2Sn-1=an-1+an-1 ,∴2an= an+an -（an-1+an-1）,∴an-an=an-1+an-1 ∴ an -an-1=an+an-1 ∴an-an-1=1 由2Sn=an+an,n=1时,2s1=a1+a1,2a1=a1+a1 a1=1 综上,an=n