Question

等比数列前n项和的练习题

Answer 1

根据题意,有S7=a1(1-q的7次方)/1-q,S14=a1(1-q的14次方)/1-q,S21=a1(1-q的21次方)/1-q所以,S14-S7=a1q的7次方(1-q的7次方)/1-q.,S21-S14=a1q的14次方(1-q的7次方)/1-q.,所以,S14-S7/S7=S21-S14/S14-S7=q的7次方所以,...