# Homework Help: Divergent Series Proof

1. Apr 14, 2014

### analysis001

1. The problem statement, all variables and given/known data
Prove that the series diverges: $\sum_{i=1}^{\infty}\sqrt{n+1}-\sqrt{n}$

3. The attempt at a solution
I'm trying to use the comparison test, but I don't know what to compare it to. All I have done so far is change the terms to be in fraction form:
$\sqrt{n+1}$-$\sqrt{n}$=$\frac{1}{\sqrt{n+1}+\sqrt{n}}$

Any clues on what to do next would be great. Thanks!

2. Apr 14, 2014

### Dick

Try comparing with $\frac{1}{\sqrt{n+1}+\sqrt{n+1}}$. Does that converge or diverge? How is it related to your original series?

3. Apr 14, 2014

### Ray Vickson

Look at the behavior of $t_n \equiv \sqrt{n+1} - \sqrt{n}$ for large $n$. It helps to write
$$\sqrt{n+1} = \sqrt{n} \left( 1 + \frac{1}{n} \right)^{1/2}$$