因为a2,a8,a5成等差数列,所以2a8=a2+a5①.又因为a2,a8,a5是等比数列{an}的项,所以①式可化为：2a2*q^6=a2+a2*q^3,即2q^6-q^3-1=0②,令q^3=x,则②式化为：2x^2-x-1=0,解得x1=1,x2=-1/2.再将x1,x2带入q^3=x即得结果.
Sn是等比数列{an}的前n项和,a2,a8,a5成等差数列,求q
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