高一数学等比数列问题
正项数列{an}是等比数列,公比q=2,a1*a2*a3*a4*..*a18=2^30,则a3*a6*a9*a12*a15*a18=?
a1*a2*a3*a4*..*a18 =a1^18 *d^(1+2+...+17) =a1^18*2^153 =2^30 ===>a1^18 =2^(-123) a3*a6*a9*a12*a15*a18=a1^6 *d^(2+5+8+11+14+17) =a1^6*2^57 a1^18 =(a1^6)^3=2^(-123) ===>a1^6 =2^(-41) ===>a1^6*2^57=2^18
答:logan-bn=loga1-b1(1) --->logan-loga1=bn-b1【在本题的解答中,均省去底数x。】 {an}是等比数列 --->an=a1*...详情>>
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