已知Sn为数列{an}的前n项和,且Sn=2an+n2-3n-2,n=1,2,3…. (Ⅰ)求证:数列{an-2n}为等比数列; (Ⅱ)设bn=an?cosnπ,求数列{bn}的前n项和Pn; (Ⅲ)设cn=,数列{cn}的前n项和为Tn,求证:Tn<. |
与“已知Sn为数列{an}的前n项和,且Sn=2an+n2-3n-2,n=1,2,3….(Ⅰ)求证:数列{an-2n}为等比数列;(Ⅱ)设bn=an•cosnπ,求数列{bn}的前n项和Pn;(Ⅲ)设cn=1an-n,数列{cn}的前n项和为”考查相似的试题有: