Given $a$ and $b$ irrational numbers with $a/b$ also irrational, how do you prove that $( \{ na\} , \{ nb \})$ is dense in $[0,1] * [0,1]$ , where $n$ ranges over the integers?

$\{x\}$ is the fractional part of $x$ .

I'm also curious about the general case, with $n$ irrational numbers , linearly independent over $Q$ , resulting in density over $[0,1]^n$ .