已知等比数列an}中,a2=2,a5=16,求a8及前六项和s6？解：a2=2，a5=16q³=a5/a2=16/2=8q=2a8=a5·q³=16·2³=128a1=a2/q=2/2=1S6=a1(q^6 -1 /(q-1 =2·(2^6 -1 /(2-...