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高中数学等比数列典型例题素材【例1】已知na为等比数列,162,262aa,则10a.【解析】方法1:811622451612qqaaqaa∴1312281162469110qaqaa方法2:812162264aaq,13122811624610qaa方法3:na为等比数列13122216222261026102aaaaaa【例2】等比数列na中,252aa,341aa,求数列na的通项公式.【解析】方法1:设公比为q,251231121aqaqaq解得11814122aaqq或则1124nna或1182nna方法2:设公比为q,知25342aaaa。343421aaaa解得3412aa或3421aa进而求出1a和q.【例3】已知等比数列na满足0,1,2,nan,且25252(3)nnaan,则当1n时,212221logloglognaaa()A.(21)nnB.2(1)nC.2nD.2(1)n【解析】由25252(3)nnaan得nna222,0na,则nna2,3212loglogaa2122)12(31lognnan,选C.【例4】等比数列同时满足下列三个条件:⑴1611aa⑵93243aa⑶三个数94,,324232aaa成等差数列.试求数列na的通项公式。【解析】1634aaaa,23323193261616161qaaaaaa或213133261qaa又94,,324232aaa成等差数列,943224223aaa…………①当311a时,38,34324312aaqaa代入①94383232)34(22(成立),.231111nnnqaa当213321qa时,不成立..231111nnnqaa
本文标题:高考数学题型全归纳:等比数列典型例题(含答案)
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