Question

等比数列{an}的首项为a1,公比为q,

Answer 1

(1)S1→3=a1(1+q+q^2)=a1*(1-q^3)/(1-q)

S4→6=a4(1+q+q^2)=a1*(1-q^3)/(1-q)*q^3

S7→9=a7(1+q+q^2)=a1*(1-q^3)/(1-q)*q^6

S7→9/S4→6=S4→6/S1→3=q^3

还是等比