郭敦顒回答：设公比为r＞0且r≠1,则a= a,b= ar,c= ar²,r=b/a.∵当r＞1时a+b＞c,∴a+ar ＞ar²,1+r ＞r²,r²－r－1＜0,解得r≤1.618；当r＜1时,a＜b+c,1＜r+r²,解得r≥0619,∴0.619≤r≤1.618...