3.设数列{an}的前n项和Sn=2an-4(n∈N+),数列{bn}满足:bn+1=an+2bn,且b1=2.求{bn}前n项的和Tn.

1.S(n)-S(n-1)=2(a(n)-a(n-1))=anan=2a(n-1)S1=2a1-4=a1====>a1=4,an=2的n+1次方2.bn+1=an+2bn=2bn+(2的n+1次方)左右两边同除以2的n+1次方====〉bn+1/2的n+1次方=[bn/(2的n次方)]+1即bn/(2的n次方)为等差数列,首项为...