4、(A)15(B)12(C)D)4.设{}为等差数列,公差d=-2,为其前n项和.若,则=()A.18B.20C.22D.245.(2008四川)已知等比数列中,则其前3项的和的取值范围是()A. B. C. D.6.(2008福建)设{an}是公比为正数的等比数列,若n1=7,a5=16,则数列{an}前7项的和为()A.63B.64C.127D.12857.(2007重庆)在等比数列{an}中,a2=8,a5=64,,则公比q为( )A.2B.3C.4D.88.若等比数列{an}满足anan