# Math Help - converges or diverges

1. ## converges or diverges

$
\sum_1^{\infty} \frac{1}{\sqrt{{k^4}+3k}}
$

what test would u use for this? i'm thinking its prolly a telescoping series but i have no idea what to do.

2. $\frac{1}{{\sqrt {k^4 + 3k} }} < \frac{1}{{k^2 }}$

3. thats not true though...k^4 i < (k^4+3K)^1/2 .... does this prove divergance?

4. Hello,

$k^4+3k>k^4$

$\sqrt{k^4+3k}>\sqrt{k^4}=k^2$ because $f:x\mapsto \sqrt{x}$ is an increasing function.

$\frac{1}{\sqrt{k^4+3k}}<\frac{1}{k^2}$ because $g:x\mapsto \frac{1}{x}$ is a decreasing function.

And we know that $\sum \frac{1}{k^a}$ converges if $a>1$