Solve: x^2 - 9 = 0

• A. x = 9 or x = -9
• B. x = 3 or x = -3
• C. x = 0 or x = 9
• D. x = -9 or x = 9

Answer: (B)

This question tests solving a quadratic by factoring. Recognize x^2 - 9 as a difference of squares: x^2 - 9 = (x - 3)(x + 3). For the product to be zero, either x - 3 = 0 or x + 3 = 0, giving x = 3 or x = -3. Those values make the left side zero, satisfying the equation. The other numbers in the choices don’t work because substituting them into x^2 - 9 doesn’t yield zero (for example, x = 9 gives 81 - 9 = 72, and x = 0 gives 0 - 9 = -9).