等比数列例题请问 {an}为等差数列,公差d不等于0,a1 a3 a9 成等比,求a1+a3+a9\a2+a4+a10
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![等比数列例题请问 {an}为等差数列,公差d不等于0,a1 a3 a9 成等比,求a1+a3+a9\a2+a4+a10](/uploads/image/z/8906444-44-4.jpg?t=%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%E4%BE%8B%E9%A2%98%E8%AF%B7%E9%97%AE+%7Ban%7D%E4%B8%BA%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%2C%E5%85%AC%E5%B7%AEd%E4%B8%8D%E7%AD%89%E4%BA%8E0%2Ca1+a3+a9+%E6%88%90%E7%AD%89%E6%AF%94%2C%E6%B1%82a1%2Ba3%2Ba9%5Ca2%2Ba4%2Ba10)
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等比数列例题请问 {an}为等差数列,公差d不等于0,a1 a3 a9 成等比,求a1+a3+a9\a2+a4+a10
等比数列例题
请问 {an}为等差数列,公差d不等于0,a1 a3 a9 成等比,求
a1+a3+a9\a2+a4+a10
等比数列例题请问 {an}为等差数列,公差d不等于0,a1 a3 a9 成等比,求a1+a3+a9\a2+a4+a10
a3^2=a1*a9
a3^2=(a3-2d)(a3+6d)
a3^2=a3^2+6da3-2da3-12d^2
4da3-12d^2=0
4d(a3-3d)=0
因为d不等于0,所以 a3-3d=0 a3=3d
a1+a3+a9\a2+a4+a10 =d+3d+9d/2d+4d+10d=13/16