设首项为a1,公比为r,当r＝1时,Sn＝n(a1),此时Sn/S(n+1)的极限为1r≠1时,Sn＝a1(1-r^n)/(1-r),Sn/S(n+1)＝(1-r^n)/(1-r^(n+1)),极限为1,则|r|＜1.因为|r|＞1时,极限是1/r所以,若lim(Sn/Sn+1)=1,求公比范围是(-1,1]...