(1)
an=(√2)^n ,a1=√2
{an}是等比数列
Sn = √2[(√2)^(n+1) -1]/(√2-1)=(2√2+2)[2^(n/2) -√2/2]
(2) an=(√2)^(n-1) ,a1=1
Sn = [(√2)^n -1]/(√2-1)=(√2+1)[2^(n/2) -1]