数学 答案及过程

学习 时间:2023-03-30 06:03:32 阅读:57
数学 答案及过程

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威武的雪糕

贪玩的芝麻

2023-03-30 06:03:32

C-------------------------------当 n = 3,a5 * a1 = 2^6即 a1^2 q^4 = 2^6----(1)当 n = 4 ,a5 * a3 = 2^8即 a1^2 * q^6 = 2^8----(2)解得 q = 2,q = -2(因为an>0,舍去)a1 = 2,a3 = 2^3,a5 = 2^5。a(2n-1) = 2^(2n-1) log2 a1 + log2 a3 +。。+ log2 a(2n-1)=log2 2 + log2 2^3 +。。+ log2 2^(2n-1)=1 + 3 +。+ (2n-1)=[ 1 + (2n-1) ] * n / 2=n^2

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  • 热心的咖啡
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    2023-03-30 06:03:32

    C-------------------------------当 n = 3,a5 * a1 = 2^6即 a1^2 q^4 = 2^6----(1)当 n = 4 ,a5 * a3 = 2^8即 a1^2 * q^6 = 2^8----(2)解得 q = 2,q = -2(因为an>0,舍去)a1 = 2,a3 = 2^3,a5 = 2^5。a(2n-1) = 2^(2n-1) log2 a1 + log2 a3 +。。+ log2 a(2n-1)=log2 2 + log2 2^3 +。。+ log2 2^(2n-1)=1 + 3 +。+ (2n-1)=[ 1 + (2n-1) ] * n / 2=n^2

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