What is the vertex of the graph of the function f(x) = x2 + 8x − 2 ?

For f(x) = x² + 8x − 2, the vertex’s x-coordinate is −b/(2a) = −8/(2 × 1) = −4. Substituting −4 gives f(−4) = 16 − 32 − 2 = −18, so the vertex is (−4, −18), choice D.

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