Advanced Math practice question

Answer: A. 6x + 18

Factor out (x + 3): (x + 3)[(x + 3) − (x − 3)] = (x + 3)(6) = 6x + 18. (Or expand: x² + 6x + 9 − (x² − 9) = 6x + 18.)

Why the other answers are wrong

B. 6x

6x drops the constant: x² + 6x + 9 minus x² − 9 leaves 6x + 18, since subtracting −9 adds 9.

C. 2x² + 18

2x² + 18 ADDS the two x² terms; they cancel when the second product is subtracted.

D. 18

18 is just the constant part; the 6x term remains.

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