设等比数列an的公比q=1⼀2 前n项和为sn 则s5⼀a3

2025-06-22 18:50:49
推荐回答(1个)
回答1:

S5/a3
=[a1(1-q⁵)/(1-q)]/(a1q²)
=(1-q⁵)/[q²(1-q)]
=(1-½⁵)/[½²(1-½)]
=(31/32)/(1/8)
=31/4