a1=1,an=(1/2)x(4/3)^(n-2)n>=2则a2n=(1/2)x(4/3)^(2n-2) n=1,2,3,4,5.
则和为；（1/2)^nx[3x(4/3)^n-3]
设数列｛an｝前n项和为Sn,且a1＝1,a（n＋1）＝1／3sn,n＝1,2,3……,求a2＋a4＋a6＋……＋a2n的值
设数列｛an｝前n项和为Sn,且a1＝1,a（n＋1）＝1／3sn,n＝1,2,3……,求a2＋a4＋a6＋……＋a2n的值
数学人气：913 ℃时间：2020-02-03 04:38:06
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