Question

数列{an}中，a3=1,a1+a2+```+an=a(n+1)下标，（n=1,2,3```)

1、求a1,a2
2、求数列{an}的前n项和Sn

Answer 1

n=1 a1=a2
n=2 a1+a2=a3
2a1=2a2=a3=1
a1=a2=0.5

a1+a2+```+an=a(n+1)
sn=a(n+1)=s(n+1)-s(n)
s(n+1)=2s(n)
s(1)=0.5
s(n)=2^(n -2)