To solve the equation \( x^2 = 81 \) using inspection, we look for values of \( x \) that, when squared, equal 81.
The square root of 81 is 9, so:
- \( x = 9 \)
- \( x = -9 \) (since squaring a negative number also results in a positive)
Therefore, the complete solution set is:
\({-9, 9}\)
So the correct response is:
\({-9, 9}\)