S=a,aq,aq^2,aq^3.aq^n (1)
qS=aq,aq^2,aq^3...aq^(n+1) (2)
(2)-(1)得
(q-1)S=aq^(n+1)-a
S=[aq^(n+1)-a]/(q-1) S=a,aq,aq^2,aq^3.aq^n (1)
qS=aq,aq^2,aq^3...aq^(n+1) (2)
(2)-(1)得
(q-1)S=aq^(n+1)-a
S=[aq^(n+1)-a]/(q-1)