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《高三数学数列小练习.docx》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、第9周晚自习考试(周一)1.数列1,3,6,10,15,⋯的通项公式an等于()A.n2(n1)B.n(n1)C.n(n1)D.n22n2222.一个等比数列的前n项和为48,前2n项和为60,则前3n项和为()A.183B.108C.75D.633.等差数列{an}和{bn}的前n项和分别为S和Tn,对一切自然数n都有nSn2na5等于()Tn3n,则1b5A.2B.9C.20D.1131431174.在各项都为正数的等比数列an中,若a5a69,则log3a1log3a2Llog3a10().A.12B.10C.8D.2log3
2、55.已知等比数列{an}的各项均为正数,公比q1,设Pa3a9,Q=a5a7,2则P与Q的大小关系是()A.P>QB.P3、函数f(x)的反函数f1(x)及其定义域;(2)数列an满足an1f1(an)(nN)ana,数列bn的前na13a,设bnana项和为Sn,试比较Sn与7的大小,并证明你的结论.810.解:(1)由已知得:xy2a2,∵yxyy2a2(ya)(ya)0,2y2y2y∴ya或ay0,∴f1(x)x2a2(ax0或xa).2xan2a2,∴bn1an2a2aa)22an(an(2)由an1f1(an)bn2,2anan2a2a(ana)22an∴lgbn12lgbn,∴lgbn是等比数列.∵lgb1lga1alg2alg2,a1a4a4、lg12n1∴lgbnlg22n1,22n1∴bn1,∵2n1n1(n4),当n4时,22n1n1bn11,2211245n1Snb1b2Lbn1112222L211n2111162.24112311n27.1317,故S482488n8
3、函数f(x)的反函数f1(x)及其定义域;(2)数列an满足an1f1(an)(nN)ana,数列bn的前na13a,设bnana项和为Sn,试比较Sn与7的大小,并证明你的结论.810.解:(1)由已知得:xy2a2,∵yxyy2a2(ya)(ya)0,2y2y2y∴ya或ay0,∴f1(x)x2a2(ax0或xa).2xan2a2,∴bn1an2a2aa)22an(an(2)由an1f1(an)bn2,2anan2a2a(ana)22an∴lgbn12lgbn,∴lgbn是等比数列.∵lgb1lga1alg2alg2,a1a4a
4、lg12n1∴lgbnlg22n1,22n1∴bn1,∵2n1n1(n4),当n4时,22n1n1bn11,2211245n1Snb1b2Lbn1112222L211n2111162.24112311n27.1317,故S482488n8
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