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

For choice C, expand or use the axis of symmetry of its roots: the zeros are 5 and −1, so the vertex’s x-coordinate is their midpoint, (5 + (−1))/2 = 2. Substituting x = 2 gives f(2) = (2 − 5)(2 + 1) = (−3)(3) = −9. Therefore, choice C, f(x) = (x − 5)(x + 1), has vertex (2, −9).

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