Hi all,

Can anybody show that the function $\displaystyle f: R^N \rightarrow R $ is convex, where:

$\displaystyle

f(x) = \frac{K + \sum_{i=1}^N x_i^2 }{ \sum_{i=1}^N x_i }

$

And $\displaystyle x_i \geq 0, \forall i$ and $\displaystyle K > 0$

Any help is welcome (this is not homework!).

Thanks!