记Sn为等比数列{an}的前n项和.若a5–a3=12,a6–a4=24,则=( )A.2n–1 ... 问题详情:记Sn为等比数列{an}的前n项和.若a5–a3=12,a6–a4=24,则=( )A.2n–1 B.2–21–n C.2–2n–1 ...