Appoint all the pairs (k, l) (both k and l $\displaystyle \in R^{+}$) such that:

$\displaystyle \sqrt{k}+\sqrt{l}=\sqrt{4+\sqrt{7}}$

I'm really stuck at it. First of all, I think that getting rid of the roots may be a good idea so we have:

$\displaystyle k+l+2\sqrt{kl}=4+\sqrt{7}$

And I don't know what to do next.. Can I please get a little help?