设数列{An}的前n项和为Sn若An+1=3Sn,a1=1则a6=
1个回答
a=3Sn,①
n=1时a2=3S1=3a1=3,
n>1时an=3S,②
①-②,a-an=3an,
a=4an,
∴a6=a2*4^4=3*256=768.
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