In the equal ratio sequence an, Sn = a1 + A2 + a3=______ fast

In the equal ratio sequence an, Sn = a1 + A2 + a3=______ fast

a4-a3=2s3+1-(2s2+1)=2s3-2s2=2a3
a4=2a3+a3=3a3
q=3