# Math Help - Geometric and Arthmetic terms

1. ## Geometric and Arthmetic terms

Find the sum of the first 29 terms 4,8,16,32

2. Originally Posted by amandaggogo

Find the sum of the first 29 terms 4,8,16,32
As $U_{n+1} = 2U_n$ then you have a geometric sequence with $\text{a = 4, n = 29, r = 2}$

The formula for the sum of a geometric sequence is

$S_n = \frac{a(r^n-1)}{r-1}$. Sub in your values and solve

Spoiler:
$S_{29} = \frac{2(2^{29}-1)}{2-1} = 1 073 741 822$

3. Thank you very much, that makes much more sense now :0)