In my mathematics class we learned radicals and how to simplify them. However some of the questions involved prime numbers that were in the radical, and we had to simplify them.
For example:
How on earth can we simplify radicals that have prime numbers in them?
$$11-6 \sqrt{2}=9+2-6 \sqrt{2}=\left(3-\sqrt{2}\right)^2\to \sqrt{11-6 \sqrt{2}}=3-\sqrt 2$$ $$11+4\sqrt6=8+3+4\sqrt{2\cdot 3}=\left(2\sqrt 2+\sqrt 3\right)^2\to \sqrt{11+4\sqrt6}=2\sqrt 2+\sqrt 3$$