Which function has a vertex at (2, –9)?

For choice C, the zeros are x = 5 and x = −1, so the vertex lies halfway between them at x = (5 + (−1))/2 = 2. Substituting x = 2 gives f(2) = (2 − 5)(2 + 1) = (−3)(3) = −9. Thus f(x) = (x − 5)(x + 1) has vertex (2, −9).

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