Algebra 1: Common Core (15th Edition)

To see if a radical is in simplified form, we see if any of its factors are perfect squares (which means that their square root will be an integer). Consider $\sqrt 12$. It has factors of 3 and 4. 3 is not a perfect square, but 4 is. Thus, we know we can simplify $\sqrt 12$ to $2\sqrt 3$.