記Sn為等比數列{an}的前n項和.若a5–a3=12,a6–a4=24,則=( )A.2n–1 ... 問題詳情:記Sn為等比數列{an}的前n項和.若a5–a3=12,a6–a4=24,則=( )A.2n–1 B.2–21–n C.2–2n–1 ...