Question

求等比数列1,2,4,...从第6项到第10项的和.

Answer 1

等比数列1,2,4,...
首项是1,公比是2
∴ 通项公式是an=1*2^(n-1)=2^(n-1)
则a6+a7+a8+a9+a10
=2^5+2^6+2^7+2^8+2^9
=(2^5-2^9 *2)/(1-2)
=(32-1024)/(-1)
=992