Question

已知数列an的前n项和Sn=-an-(1/2)^(n-1)+2

Answer 1

1)

Sn=-an-1/2^n-1+2

Sn+1=-an+1-1/2^n+2

Sn+1-Sn=an+1=-an+1+an+1/2^n

2an+1=an+1/2^n

2^(n+1)an+1=2^nan+1

bn+1=bn-2 数列{bn}是等差数列

an=n/2^n