To solve the equation \( p^2 = 9 \), we can take the square root of both sides.
Taking the square root gives us:
\[ p = \sqrt{9} \quad \text{or} \quad p = -\sqrt{9} \]
Calculating the square root of 9:
\[ p = 3 \quad \text{or} \quad p = -3 \]
Thus, the solutions for \( p \) are:
\[ p = 3 \quad \text{or} \quad p = -3 \]
These can be expressed as:
\[ p = 3, -3 \]
So the final answers are:
\[ \boxed{3} \quad \text{and} \quad \boxed{-3} \]