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