13题.数列13题.数列
13题.数列Sn=2an-1 S(n+1)=2a(n+1)-1S(n+1)-Sn=a(n+1)=2a(n+1)-2ana(n+1)=2an当n=1时a1=2a1-1a1=1{an}是以1为首项,2为公比的G.P.an=1*2^(n-1)=2^(n-1)