Advanced Math practice question

Answer: A. x = 3

A parabola is symmetric about the vertical line midway between its x-intercepts. The midpoint of −1 and 7 is (−1 + 7)/2 = 3, so the axis is x = 3.

Why the other answers are wrong

B. x = 6

6 is 7 − 1 — the difference of the intercepts, not their midpoint. Average them: (−1 + 7)/2.

C. x = −4

−4 is (−1 − 7)/2, subtracting instead of adding. The midpoint adds the two values before halving.

D. x = 4

4 is half the distance between the intercepts (8/2). The axis is at the midpoint, which is −1 + 4 = 3, not 4 itself.

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