1.已知数列{an},{bn}满足a1=2,a2=4,bn=a(n+1)-an,b(n+1)=2bn+2.(1)求证:数列{bn+2}是公比为2的等比数列;(2)求an.注:a(n+1)中(n+1)为a的角标,后同.2.已知数列{an}是等差数列,且a1=2,a1+a2+a3=12(
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