Start by making a factor tree for 18.
18 factors as 6 x 3 and 6 factors as 2 x 3.
Look for pairs of factors that are the same.
In this case, the 3's match up.
So a 3 will come out of the radical.
Whatever does not pair up stays inside.
In this case, the 2 goes inside.
So our answer is 3√2.
