等比数列an中,a1+a2+a3=6,a4+a5+a6=18,则a10+a11+a12=?
问题描述:
等比数列an中,a1+a2+a3=6,a4+a5+a6=18,则a10+a11+a12=?
答
162
a1(1+q+q^2)=6
a1q^3(1+q+q^2)=18
q^3=3
a10+a11+a12=a1q^9((1+q+q^2)=162