1、2.4 等比数列2.4.1 等比数列的概念与通项公式►基础达标1.在数列{an}中,对任意n∈N*,都有an+1-2an=0,则的值为( )A. B. C. D.1解析:a2=2a1,a3=2a2=4a1,a4=8a1,∴==.故选A.答案:A2.在等比数列中,a1=,an=,q=,则项数n为( )A.3B.4C.5D.6解析:由a1qn-1=an⇒·=⇒n=4.答案:B3.等差数列{an}的首项a1=1,公差d≠0,如果a1,a2,a5成等比数列,那么d等于( )A.3B.2C.-2D.2或-2解析:由a=a1a5⇒(a1+d)2=a1(a1+4d)⇒(1+