设等比数列an的公比是q=2,前an项的和为sn,则s4/a2=?

设等比数列an的公比是q=2,前an项的和为sn,则s4/a2=?
设等比数列an的公比是q=2,前an项的和为sn,则s4/a2=?

设等比数列an的公比是q=2,前an项的和为sn,则s4/a2=?
sn=(1(1-q^n))/(a1*q)
a2=a1*q
s4/a2=(a1(1-q^n))/(a1×q(1－q))＝(1-q^n)/(q(1－q))＝(2^n－1)/2