Geometric Sequences

Oct 2015
1
0
Australia
How many terms of the geometric sequence 1.2, 2.4, 4.8, 9.6, 19.2...are required for the sum to be greater than 10,000?

Do you use the equation sn=a(1-r^n)/1-r? And how is logarithms included in this question?
 

Plato

MHF Helper
Aug 2006
22,458
8,632
How many terms of the geometric sequence 1.2, 2.4, 4.8, 9.6, 19.2...are required for the sum to be greater than 10,000?
Do you use the equation sn=a(1-r^n)/1-r? And how is logarithms included in this question?
Please supply some samples of your own efforts so that we may help you.

Hint: use \(\displaystyle \log_{10} \) because \(\displaystyle {S_n} > 10^5 \) .
 

HallsofIvy

MHF Helper
Apr 2005
20,249
7,909
You want \(\displaystyle S_n> 10^4= 10,000\).