设等差数列{an}的公差为d,∵ a1,a3,a9成等比数列∴ a3²=a1*a9∴ (a1+2d)²=a1*(a1+8d)∴ a1²+4a1d+4d²=a1²+8a1d∴ 4d²=4a1d∵ d≠0∴ a1=d∴ an=a1+(n-1)d=nd∴ （a1＋a3＋a9）除（a2...