# Geometric Series - Find it's sum

• Sep 25th 2011, 02:04 PM
l flipboi l
Geometric Series - Find it's sum
Can you verify if my answer is correct for this problem?

• Sep 25th 2011, 02:33 PM
Soroban
Re: Geometric Series - Find it's sum
Hello, l flipboi l

Quote:

Can you verify if my answer is correct for this problem?

. . $\sum^{\infty}_{n=0} \frac{1}{(\sqrt{5})^n}$

$\text{Answer: }\:\frac{\sqrt{5}}{\sqrt{5}-1}$ . Yes!

$\text{Infinite geometric series with first term }a = 1\,\text{ and common ratio }r = \tfrac{1}{\sqrt{5}}$

. . $\text{Sum} \:=\:\frac{a}{1-r} \;=\;\frac{1}{1-\frac{1}{\sqrt{5}}} \;=\;\frac{\sqrt{5}}{\sqrt{5}-1}$
• Sep 25th 2011, 04:51 PM
Re: Geometric Series - Find it's sum
Quote:

Originally Posted by l flipboi l
Can you verify if my answer is correct for this problem?

$S=\frac{1}{\sqrt{5}^0}+\frac{1}{\sqrt{5}^1}+...... .$

$S-1=\frac{1}{\sqrt{5}^1}+\frac{1}{\sqrt{5}^2}+.....$

$\sqrt{5}(S-1)=1+\frac{1}{\sqrt{5}^1}+....$

$\sqrt{5}S-\sqrt{5}=S$

$S\left(\sqrt{5}-1\right)=\sqrt{5}$

$S=\frac{\sqrt{5}}{\sqrt{5}-1}$
• Sep 25th 2011, 07:04 PM
l flipboi l
Re: Geometric Series - Find it's sum
Thank you, both!