Solve x^2 - 9 = 0.

Solve x^2 - 9 = 0.

• A. x = 9 or x = -9
• B. x = 0 or x = 0
• C. x = 3 or x = -3
• D. x = 1 or x = -1

Answer: (C)

This tests solving a quadratic by recognizing a difference of squares. 9 is 3^2, so x^2 - 9 factors as (x - 3)(x + 3). Setting this equal to zero and using the zero-product property means either x - 3 = 0 or x + 3 = 0, giving x = 3 or x = -3. Those values satisfy the original equation because 3^2 - 9 = 0 and (-3)^2 - 9 = 0. If you try other values: x = 9 or -9 makes x^2 - 9 = 72, not 0; x = 0 gives -9; x = 1 or -1 gives -8.

This tests solving a quadratic by recognizing a difference of squares. 9 is 3^2, so x^2 - 9 factors as (x - 3)(x + 3). Setting this equal to zero and using the zero-product property means either x - 3 = 0 or x + 3 = 0, giving x = 3 or x = -3. Those values satisfy the original equation because 3^2 - 9 = 0 and (-3)^2 - 9 = 0.

If you try other values: x = 9 or -9 makes x^2 - 9 = 72, not 0; x = 0 gives -9; x = 1 or -1 gives -8.