The expression you need to simplify is $\sqrt{18}$. Let's break it down.

We can express $18$ as a product of perfect squares:

$\sqrt{18} = \sqrt{9 \times 2} = \sqrt{9} \times \sqrt{2} = 3\sqrt{2}$

So, $\sqrt{18}$ simplifies to:

$3\sqrt{2}$

Would you like a further explanation on the steps? Here are some related questions:

1. How do you simplify other square roots involving non-perfect squares?
2. What is the difference between simplifying $\sqrt{18}$ and estimating its decimal value?
3. Can all square roots be simplified in this way?
4. What are examples of other square roots that simplify similarly to $\sqrt{18}$?
5. How can simplifying square roots help in solving larger algebraic problems?

Tip: Always look for the largest perfect square factor of a number when simplifying square roots.