Factor $12=2^{2}\times 3$. Rewrite the square root of the product $\sqrt{2^{2}\times 3}$ as the product of square roots $\sqrt{2^{2}}\sqrt{3}$. Take the square root of $2^{2}$.
$$2\sqrt{3}\sqrt{15}$$
Factor $15=3\times 5$. Rewrite the square root of the product $\sqrt{3\times 5}$ as the product of square roots $\sqrt{3}\sqrt{5}$.
