摘要:19.已知,¬是¬的必要不充分条件.求实数的取值范围.
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(本小题满分12分)已知等差数列{an}的前
n项和为Sn,且a3=5,S15="225."
(Ⅰ)求数列{an}的通项an;
(Ⅱ)设bn=
+2n,求数列{bn}的前n项和Tn.
(本小题满分12分)已知等差数列{an}的前n项和为Sn,且a3=5,S15=225.
(Ⅰ)求数列{an}的通项an;
(Ⅱ)设bn=
+2n,求数列{bn}的前n项和Tn.
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