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Advanced MathHardAxis of symmetry and minimum from factored form

Advanced Math practice question

The function q is defined by q(x) = (x − 5)(x + 1). Which statement is true about the graph of y = q(x)?

  1. A. Its axis of symmetry is x = 2 and its minimum value is −9.Correct
  2. B. Its axis of symmetry is x = 2 and its minimum value is −5.
  3. C. Its axis of symmetry is x = −2 and its minimum value is −9.
  4. D. Its axis of symmetry is x = 3 and its minimum value is −8.

Answer: A. Its axis of symmetry is x = 2 and its minimum value is −9.

The zeros are 5 and −1; the axis is their midpoint, x = 2. q(2) = (−3)(3) = −9.

Why the other answers are wrong

B. Its axis of symmetry is x = 2 and its minimum value is −5.
−5 is the y-intercept, q(0), not the minimum.
C. Its axis of symmetry is x = −2 and its minimum value is −9.
The midpoint of 5 and −1 is 2, not −2.
D. Its axis of symmetry is x = 3 and its minimum value is −8.
x = 3 is not midway between the zeros.

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