A map from $\Bbb R$ to the torus

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Suppose $a,b\in \Bbb R$, we have a map $f:\Bbb R \to \Bbb T$ which is defined as following:

$f(t)=(at \mod 1,bt \mod 1)$

Is $f(\Bbb R)$ dense in $\Bbb T$?

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What do you think? You can gain some intuition by drawing some sketches on the unit square. What does the image of $f$ look like when $(a,b)=(1,1)$? What about $(a,b) =(\sqrt{2}, 1)$?