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

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