设数列{an}的前n项和为Sn,已知a1=a(a≠3),Sn+1=2Sn+3n,
题型:解答题
问题:
设数列{an}的前n项和为Sn,已知a1=a(a≠3),Sn+1=2Sn+3n,n∈N*.
(1)设bn=Sn-3n,n∈N*,证明数列{bn}为等比数列;
(2)求数列{an}的通项公式;
(3)若an+1≥an,n∈N*,求a的取值范围.
设数列{an}的前n项和为Sn,已知a1=a(a≠3),Sn+1=2Sn+3n,n∈N*.
(1)设bn=Sn-3n,n∈N*,证明数列{bn}为等比数列;
(2)求数列{an}的通项公式;
(3)若an+1≥an,n∈N*,求a的取值范围.