I know how to prove that the $\displaystyle \sqrt{2}$ is irrational, and that $\displaystyle \sqrt{3}$ is irrational. But how does one go about using the tricks involved in the $\displaystyle \sqrt{2}$ proof on something like proving that $\displaystyle P$ is irrational if:

$\displaystyle P = \sqrt{2} + \sqrt{3}$

?

Thanks in advance