∵a1、a3、a9成等比数列∴(a3)^2=a1×a9(a1+2d)^2=a1×(a1+8d)d^2=a1×d∵d≠0∴d=a1(a1+a3+a9)/(a2+a4+a10)=(3×a1+10d)/(3×a1+13d)=(13d)/(16d)=13/16
13/16
