设an是公比为2的等比数列,如果a1a2a3a4……a30=2^30,则a2a5a8……a98=
问题描述：
设an是公比为2的等比数列,如果a1a2a3a4……a30=2^30,则a2a5a8……a98=
答
S=a2a5a8a11...a98=a1q*a1q^4*a1q^7*a1q^10*.*a1q^97 (一共有33项S=a1^33q^(1+4+7+10+...+97)=a1^33q^[(1+97)33/2]=a1^33q^(49*33)a1a2a3a4.a30=a1a1qa1q^2...a1q^29=a1^30q^[(1+29)*30/2]=a1^30*2^(30*15)=2^30(a12...