To express the solutions to the equation \( x^2 = 18 \) in set notation, we can first note the solutions you've mentioned, which are \(-6\) and \(6\). However, it seems there has been a small oversight because when solving \( x^2 = 18 \), the actual solutions should be:
\[ x = \pm \sqrt{18} = \pm 3\sqrt{2} \]
Thus, the correct solutions to the equation \( x^2 = 18 \) are \( -3\sqrt{2} \) and \( 3\sqrt{2} \).
Now, in set notation, we want to list these solutions from least to greatest. Therefore, the solution set is:
\[ { -3\sqrt{2}, 3\sqrt{2} } \]
If you were only considering \(-6\) and \(6\), then the set notation for those numbers would be:
\[ { -6, 6 } \]
However, please ensure you're referring to the correct solutions based on the equation provided.