Question what-i

2.1 Nonlinear Functions - Quadratic graphs and vertex form
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What is the minimum value of the function f defined by f of x equals, open parenthesis, x minus 2, close parenthesis, squared, minus 4  ?

A.

negative 4

B.

negative 2

C.

2

D.

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, f of x equals, open parenthesis, x minus h, close parenthesis, squared, plus k , where the point with coordinates h comma k is the vertex of the graph of y equals f of x in the xy-plane. Therefore, the vertex of the graph of y equals f of x is the point with coordinates 2 comma negative 4. 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 open parenthesis, x minus 2, close parenthesis, squared) is 1, which is positive, the graph of y equals f of x opens upward. It follows that at x equals 2 , the minimum value of the function f is negative 4 .

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.