Answer
$\sqrt3 \cdot \sqrt{12} = \sqrt{36} = 6$
$\sqrt3$ and $\sqrt{12}$ are irrational numbers, but 6 is not.
Work Step by Step
Irrational numbers are not closed with respect to multiplication, as can be seen in the example below:
$\sqrt3$ and $\sqrt{12}$ are irrational numbers.
However, $\sqrt3 \cdot \sqrt{12} = \sqrt{36}=6$, which is not an irrational number.