【课时精练】√1.若等差数列{an}的首项为1,公差为1,等比数列{bn}的首项为-1,公比为-2,则数列{an+bn}的前8项和为 A.-49 B.-219 C.121 D.291因为等差数列{an}的首项为1,公差为1,等比数列{bn}的首项为-1,公比为-2,记等差数列{an}的前n项和为Sn,等比数列{bn}的前n项和为Tn,√2.设Sn是等比数列{an}的前n项和,若S4=6,S8=18,则S16=A.48 B.90 C.96 D.162设等比数列{an}的公比为q,当q=1时,S4=4a1=6,S8=8a1=18,无解,不合题意;知识梳理(1)若等比数列{a