Answer: 6√2
Step-by-step explanation: The easiest way to do this problem is to factor 72 as 2 · 36, then recognize 36 as a perfect square, 6 · 6.
There's no need to factor further because the 6's pair up
so a 6 comes out of the radical leaving a 2 inside.
So our answer is 6√2.
Always be on the lookout for perfect squares!
Work is attached below.