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

For choice C, expand or rewrite f(x) = (x – 5)(x + 1) as x² – 4x – 5. The vertex’s x-coordinate is –b/(2a) = –(–4)/(2·1) = 2; substituting x = 2 gives f(2) = (2 – 5)(2 + 1) = –9. So its vertex is (2, –9).

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