{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求q

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{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求q{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求q{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求qa4=a

{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求q
{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求q

{an}为等比数列.公比是q.-a5,a4,a6成等差数列,求q
a4=a1*q^3
a5=a1*q^4
a6=a1*q^5
a4=[a6-(-a5)]/2=(a5+a6)/2
a1*q^3=a1(q^4+q^5)/2
1=(q+q^2)/2
q^2+q-2=0
(q+2)(q-1)=0
q1 = -2
q2 = 1(不能构成等比级数)
∴q=-2