若{an}是等比数列,其公比是q,且-a5,a4,a6成等差数列,则q等于?(求详解)
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若{an}是等比数列,其公比是q,且-a5,a4,a6成等差数列,则q等于?(求详解)
等比数列,其公比是q
∴a5=q*a4,a6=q*a5=q^2*a4
-a5,a4,a6成等差数列
∴a4-(-a5)=a6-a4
a4+q*a4=q^2*a4=a4
2+q-q^2=0
(q+1)(q-2)=0
∴ q=-1
或者q=2
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