What is the y-value of the vertex of the function f(x)=−(x+8)(x−14)?

The zeros are x = −8 and x = 14, so the vertex lies halfway between them at x = (−8 + 14)/2 = 3. Substituting x = 3 gives f(3) = −(3 + 8)(3 − 14) = −(11)(−11) = 121. The y-value of the vertex is 121, choice D.

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