8-7=____
数列{an}的前n项和为Sn,若对于任意的正整数n,都有Sn=2an﹣3n.
(1)设bn=an+3,求证:数列{bn}是等比数列,并求出{an}的通项公式;
(2)求数列{nan}的前n项和.
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