Question what-i
What is the minimum value of the function f defined by ?
2
4
What is the minimum value of the function f defined by ?
Hard-difficulty · SAT Math · Nonlinear Functions — Quadratic graphs and vertex form. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.
Answer explanation
Choice A is correct. The given quadratic function f is in vertex form, , where
is the vertex of the graph of
in the xy-plane. Therefore, the vertex of the graph of
is
. In addition, the y-coordinate of the vertex represents either the minimum or maximum value of a quadratic function, depending on whether the graph of the function opens upward or downward. Since the leading coefficient of f (the coefficient of the term
) is 1, which is positive, the graph of
opens upward. It follows that at
, the minimum value of the function f is
.
Choice B is incorrect and may result from making a sign error and from using the x-coordinate of the vertex. Choice C is incorrect and may result from using the x-coordinate of the vertex. Choice D is incorrect and may result from making a sign error.
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