等比数列,a1＝2,s3＝26,求q与a3

等比数列,a1＝2,s3＝26,求q与a3
等比数列,a1＝2,s3＝26,求q与a3

等比数列,a1＝2,s3＝26,求q与a3
S3=a1+a2+a3
=a1(1+q+q^2)
2(1+q+q^2)=26
q^2+q-12=0
q=3,q=-4
a3=a1q^2=18,或a3=a1q^2=32