Irrational and rational proofs

Hey, I was wondering about proving that square roots of numbers are rational or irrational.
I know about proving this for the numbers 1(duh), 2 and all multiples of 2 and 4, but what about 3?
How do i prove that 3(or any other number) is irrational or rational?

>>13


3 isn't irrational.  3^1/2 is, and my proof shows that for all n in the natural numbers such that n isn't a square.

>>12 is an obvious extension of my proof into all kth roots of natural numbers.

>>3 is a shitty proof