What is the vertex of the graph of y = x2 + 4x?

For y = x² + 4x, the vertex’s x-coordinate is −b/(2a) = −4/(2 · 1) = −2. Substituting x = −2 gives y = (−2)² + 4(−2) = 4 − 8 = −4. The vertex is (−2, −4), choice D.

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