add or subtract a surd, swap the + or – sign and multiply the numerator and denominator by this expression. For example, if the denominator includes the bracket \((5 + 2\sqrt{3})\), then ...

Watch this video to learn about the rules of surds. For example, \(\sqrt 4 = 2\) is not a surd. However \(\sqrt 5\) is a surd. If you use a calculator, you will see that \(\sqrt 5 = 2.236067977..