The expression \( 9x^2 - 25 \) is a difference of squares. It can be factored using the formula \( a^2 - b^2 = (a - b)(a + b) \).
In this case:
- \( a^2 = 9x^2 \) which gives \( a = 3x \)
- \( b^2 = 25 \) which gives \( b = 5 \)
Applying the formula, we get:
\[ 9x^2 - 25 = (3x - 5)(3x + 5) \]
So, the factored form of the quadratic expression \( 9x^2 - 25 \) is:
\[ (3x - 5)(3x + 5) \]