设等差数列an中前n项和为sn,且s5=a5,若a4不等于0,则a7\a4=

设等差数列an中前n项和为sn,且s5=a5,若a4不等于0,则a7\a4=
设等差数列an中前n项和为sn,且s5=a5,若a4不等于0,则a7\a4=

设等差数列an中前n项和为sn,且s5=a5,若a4不等于0,则a7\a4=
s5=a5,则a1＋a2＋a3＋a4=0,则a1＋a4=0,化简有2a1＋3d=0.a7/a4=(a1＋6d)/(a1＋3d)=(2a1＋12d)/(2a1＋6d)=(9d)/(3d)=3.