# Divergent Series Proof

## Homework Statement

Prove that the series diverges: $\sum_{i=1}^{\infty}\sqrt{n+1}-\sqrt{n}$

## 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!

Dick
Science Advisor
Homework Helper

## Homework Statement

Prove that the series diverges: $\sum_{i=1}^{\infty}\sqrt{n+1}-\sqrt{n}$

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

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Ray Vickson
Science Advisor
Homework Helper
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## Homework Statement

Prove that the series diverges: $\sum_{i=1}^{\infty}\sqrt{n+1}-\sqrt{n}$

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