等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?RT.

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等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?RT.

等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?RT.
等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?
RT.

等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?RT.
等比数列{an}前三项为a1,a2=a1q,a3=a1q^2
已知S1,S3,S2成等差数列,即2S3=S1+S2
2(a1+a1q+a1q^2)=a1+a1+a1q
可解得q=-1/2
a1-a3=3
a1-a1q^2=3,可解得a1=4
将a1,q代入等比数列可求出Sn