What is the vertex of g(x) = 8x2 – 64x?

For a quadratic g(x) = ax² + bx + c, the vertex’s x-coordinate is −b/(2a). Here, that is −(−64)/(2·8) = 4; substituting x = 4 gives g(4) = 8(4²) − 64(4) = 128 − 256 = −128. The vertex is (4, −128), choice A.

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