Answer:
2√2
Explanation:
18 factors down to 3 * 3 * 2
The rule for taking the square root of a number factored into primes is if they are in pairs, take one of the pairs out of the root sign and throw the other one away. Any odd number of primes always has one prime left under the root sign.
3√2 - √2
Root 2 is a common factor on either side of the minus sign.
√2*(3 -1)
√2 * 2