设等比数列{an}的前n项和为Sn.已知a2=6,6a1+a3=30,求an和Sn
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![设等比数列{an}的前n项和为Sn.已知a2=6,6a1+a3=30,求an和Sn](/uploads/image/z/13397362-34-2.jpg?t=%E8%AE%BE%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn.%E5%B7%B2%E7%9F%A5a2%3D6%2C6a1%2Ba3%3D30%2C%E6%B1%82an%E5%92%8CSn)
设等比数列{an}的前n项和为Sn.已知a2=6,6a1+a3=30,求an和Sn
设等比数列{an}的前n项和为Sn.已知a2=6,6a1+a3=30,求an和Sn
设等比数列{an}的前n项和为Sn.已知a2=6,6a1+a3=30,求an和Sn
设公比为q,有6a1+a3=6*a2/q+a2*q=6*(6/q+q)=30,
q^2-5q+6=0,q=2或q=3
q=2时,a1=3,an=3*2^(n-1),Sn=3*(2^n-1)
q=3时,a1=2,an=2*3^(n-1),Sn=3^n-1