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1、課時(shí)跟蹤檢測(三十四) 高考基礎(chǔ)題型得分練12017四川綿陽一診已知數(shù)列an的通項(xiàng)公式是an2n3n,則其前20項(xiàng)和為()A380B400C420D440答案:C解析:令數(shù)列an的前n項(xiàng)和為Sn,則S20a1a2a202(1220)323420.2已知數(shù)列an是首項(xiàng)為1的等比數(shù)列,Sn是an的前n項(xiàng)和,且9S3S6,則數(shù)列的前5項(xiàng)和為()A.或5B或5 C. D答案:C解析:設(shè)an的公比為q,顯然q1,由題意,得,所以1q39,解得q2,所以是首項(xiàng)為1,公比為的等比數(shù)列,則所求的前5項(xiàng)和為.3數(shù)列an的通項(xiàng)公式為數(shù)列an,其前n項(xiàng)和為,則在平面直角坐標(biāo)系中,直線(n1)xyn0在y軸上的截距為
2、()A10B9 C10 D9答案:B解析:數(shù)列的前n項(xiàng)和為1,解得n9,直線方程為10xy90.令x0,得y9,在y軸上的截距為9.4數(shù)列an的通項(xiàng)公式為an(1)n1(4n3),則它的前100項(xiàng)和S100()A200B200 C400D400答案:B解析:S100(413)(423)(433)(41003)4(12)(34)(99100)3(3)3(3)4(50)200.5.的值為()A.BC. D答案:C解析:,.62017安徽合肥一模已知數(shù)列an的前n項(xiàng)和Snn26n,則|an|的前n項(xiàng)和Tn等于()A6nn2Bn26n18C. D 答案:C解析:由Snn26n,得an是等差數(shù)列,且首項(xiàng)
3、為5,公差為2.an5(n1)22n7,當(dāng)n3時(shí),an0;當(dāng)n3時(shí),an0.Tn 7已知函數(shù)f(n) 且anf(n)f(n1),則a1a2a3a100()A0B100 C100D10 200答案:B解析:由題意,得a1a2a3a1001222223232424252992100210021012(12)(32)(99100)(101100)(1299100)(23100101)5010150103100.故選B.8已知數(shù)列2 008,2 009,1,2 008,2 009,這個數(shù)列的特點(diǎn)是從第二項(xiàng)起,每一項(xiàng)都等于它的前后兩項(xiàng)之和,則這個數(shù)列的前2 017項(xiàng)和S2 017()A2 008B2 0
4、10 C1D0答案:A解析:由已知,得anan1an1(n2),an1anan1.故數(shù)列的前8項(xiàng)依次為2 008,2 009,1,2 008,2 009,1,2 008,2 009.由此可知數(shù)列為周期數(shù)列,周期為6,且S60.2 01763361,S2 017S12 008.92017湖南長沙長郡中學(xué)高三月考數(shù)列an滿足a11,對任意的nN*都有an1a1ann,則()A.B C. D答案:B解析:a11,且對于任意的nN*,an1a1ann,an1ann1,當(dāng)n2時(shí),an(anan1)(an1an2)(a2a1)n(n1)21,當(dāng)n1時(shí)也成立,an,2,數(shù)列的前n項(xiàng)和為Sn22,故選B.10
5、2017陜西寶雞模擬已知數(shù)列an的前n項(xiàng)和為Sn,對任意nN*都有Snan,若1Sk9(kN*),則k_.答案:4解析:當(dāng)n1時(shí),Sn1an1,ananan1,an2an1.又a11,an為等比數(shù)列,且an(2)n1,Sk,由1Sk9,得4(2)k28,又kN*,k4.112017湖北武漢測試在數(shù)列an中,a11,an1(1)n(an1),記Sn為an的前n項(xiàng)和,則S2 013_.答案:1 005解析:由a11,an1(1)n(an1)可得a11,a22,a31,a40,該數(shù)列是周期為4的數(shù)列,所以S2 013503(a1a2a3a4)a2 013503(2)11 005.12已知數(shù)列an滿足
6、an1,且a1,則該數(shù)列的前2 016項(xiàng)的和等于_答案:1 512解析:因?yàn)閍1,又an1,所以a21,從而a3,a41,即得ankN*,故數(shù)列的前2 016項(xiàng)和等于S2 0161 0081 512.沖刺名校能力提升練1已知數(shù)列an中,an4n5,等比數(shù)列bn的公比q滿足qanan1(n2)且b1a2,則|b1|b2|b3|bn|()A14nB4n1 C. D答案:B解析:由已知,得b1a23,q4,bn(3)(4)n1,|bn|34n1,即|bn|是以3為首項(xiàng),以4為公比的等比數(shù)列|b1|b2|bn|4n1.22017湖南常德模擬已知數(shù)列an的前n項(xiàng)和為Sn,a11,當(dāng)n2時(shí),an2Sn1n
7、,則S2 015()A2 015B2 013 C1 008D1 007答案:C解析:因?yàn)閍n2Sn1n,n2,所以an12Snn1,n1,兩式相減,得an1an1,n2.又a11,所以S2 015a1(a2a3)(a2 014a2 015)1 008,故選C.32017陜西西安質(zhì)檢已知數(shù)列an滿足a11,an1an2n(nN*),則S2 016()A22 0161B321 0083C321 0081D321 0072答案:B解析:a11,a22,又2,2.a1,a3,a5,成等比數(shù)列;a2,a4,a6,成等比數(shù)列,S2 016a1a2a3a4a5a6a2 015a2 016(a1a3a5a2
8、015)(a2a4a6a2 016)321 0083.故選B.4.對于數(shù)列an,定義數(shù)列an1an為數(shù)列an的“差數(shù)列”,若a12,an的“差數(shù)列”的通項(xiàng)公式為2n,則數(shù)列an的前n項(xiàng)和Sn_.答案:2n12解析:an1an2n,an(anan1)(an1an2)(a2a1)a12n12n2222222n222n.Sn2n12.5已知數(shù)列an是遞增的等比數(shù)列,且a1a49,a2a38.(1)求數(shù)列an的通項(xiàng)公式;(2)設(shè)Sn為數(shù)列an的前n項(xiàng)和,bn,求數(shù)列bn的前n項(xiàng)和Tn.解:(1)由題設(shè),知a1a4a2a38,又a1a49,可解得或(舍去)設(shè)等比數(shù)列an的公比為q,由a4a1q3,得q2,故ana1qn12n1,nN*.(2)Sn2n1,又bn,所以Tnb1b2bn1,nN*.6已知等比數(shù)列an的前n項(xiàng)和為Sn,公比q0,S22a22,S3a42.(1)求數(shù)列an的通項(xiàng)公式;(2)令cnTn為cn的前n項(xiàng)和,求T2n.解:(1)S22a22,S3a42,S3S2a42a2,即a3a42a2,q2q20,解得q2或q1(舍去)又a1a22a22,a2a12,a1qa12,代入q,解得a12,an22n12n.(2)cnT2n(c1c3c5c2n1)(c2c4c2n).記M1,則M1.記M2,則M2,得M222,M2.T2n.