等比数列的前n项和习题(含答案)

[A]11aa2a3n()A1a1an1111aB1an1aC.an11a1DD.a1SnnD.2{an}nSn4a12a2a3a11S4()A7B8C15D16C.{an}q4a12a2a34a24a1a34a1q4a1a1q2q24q40q2a11S41241215C.3{an}nSnS33S20q()A2B2C3D3A.S33S20a11q31q3a11q21q0(1q)(q24q4)0.q2q1()4{an}nSnS38S67a7a8a9()A.18B18C.578D558A.nS3S6S3S9S6a7a8a9S9S6S3S6S3a7a8a9a7a8a9S6S32S318.A.S6S3S3q3q3S6S3S318a7a8a9S9S6S3q6818218.A.5{an}S3013S10S10S30140S20()A90B70C40D30C.S303S10q1.S3013S10S10S30140S1010S30130a11q101q10a11q301q130q20q10120.q103S20a11q201qS10(1q10)10(13)40.6{an}q4321an________{an}321a11431421a11.an4n1.4n17{an}{an1an}{an}a11an1an2n{an}nSn________an1an2nan2n1.Sna1a2an2222nn212n12n2n1n2.2n1n28{an}a1a2a31a4a5a6215S15________{an}qq32.a1a2a3a11q(1q3)1a11q13S15a11q(1q15)a11q[1(q3)5]13[1(2)5]11.119Sn{an}nS22S36.(1){an}(2)SnSn1SnSn2(1){an}q.a11q2a11qq26.q2a12.{an}an(2)n.(2)(1)Sna11qn1q23(1)n2n13.Sn2Sn143(1)n2n32n232[23(1)n2n13]2SnSn1SnSn210{an}1{bn}a1a2a6.(1){an}(2)b1b2bk85k(1){an}da1a2a6a22a1a6(1d)21(15d)d23dd0d3an1(n1)33n2.(2){bn}1qa2a14b1b2bk14k144k13.4k13854k256k4.k4.[B]112464()A13B12C11D10B.a1a1qa1q2a1qn3a1qn2a1qn1.a31q32a31q3n64.a61q3(n1)8a21qn12a1a1qa1q2a1qn164an1qnn1264(a21qn1)n6422n642n12.12{an}10S8514S17012Sa3a6a9a12________qSSq2Sa1[1q25]1q28514a114q2.Sa3a6a9a12a3(1q3q6q9)a1q21q121q3585.58513{an}nSna11{Sn}c(c0)(1){an}(2)a2a4a2n.S1a11.(1)c1an1n1SnSn1n2?an1n10n2.c1an1n1c1cn2n2.(2)c1a2a4a2n0c1a2c2a2a4a2nc11c2n1c2c2n11c.14()1120MM26M107M75%.(1)nMan(2)Ana1a2annAn80MnM9M(1)n6{an}12010an12010(n1)13010nn7{an}a634a670an7034n6nManan13010nn67034n6n7.(2)Sn{an}n1n6Sn120n5n(n1)An1205(n1)1255nn7SnS6(a7a8an)57070344134n678021034n6An78021034n6n{an}{An}A87802103486882476480A978021034969767996809M