∵ S(n+1)-Sn=a(n+1)=3Sn
∴S(n+1)=4Sn
S(n+1)/Sn=4
则{Sn}是公比为4的等比数列
S1=a1=1
Sn=4^(n-1)
S10=4^9
∴log4S10
=log4(4^9)
=9