等比数列 已知a5=4,a7=6,求a9和a3?
问题描述:
等比数列 已知a5=4,a7=6,求a9和a3?
答
q^2=a7/a5
q^2=3/2
a9=a7q^2
=6*3/2
=9
a3=a5/q^2
=4/(3/2)
=4*2/3
=8/3