Advanced Math practice question

Answer: A. 9

One real solution means discriminant 0: 36 − 4c = 0, so c = 9. (Then (x + 3)² = 0.)

Why the other answers are wrong

B. 6

c = 6 gives discriminant 36 − 24 = 12 > 0: two solutions.

C. −9

c = −9 gives 36 + 36 = 72 > 0: two solutions.

D. 3

c = 3 gives 36 − 12 = 24 > 0: two solutions.

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