Question f-x-x-

2.2 Nonlinear Equations in One Variable - Quadratic solving (factoring, quadratic formula, completing square)
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fx= x 2 - 18 x - 360

If the given function f is graphed in the xy-plane, where y=fx, what is an x-intercept of the graph?

A.

-12,0

B.

-30,0

C.

-360,0

D.

12,0

f x = x 2 - 18 x - 360 If the given function f is

Medium-difficulty · SAT Math · Nonlinear Equations in One Variable — Quadratic solving (factoring, quadratic formula, completing square). 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. It's given that y=fx. The x-intercepts of a graph in the xy-plane are the points where y = 0 . Thus, for an x-intercept of the graph of function f , 0=fx. Substituting 0 for fx in the equation fx=x2-18x-360 yields 0 = x 2 - 18 x - 360 . Factoring the right-hand side of this equation yields 0=x+12x-30. By the zero product property, x + 12 = 0 and x - 30 = 0 . Subtracting 12 from both sides of the equation x + 12 = 0 yields x = -12 . Adding 30 to both sides of the equation x - 30 = 0 yields x = 30 . Therefore, the x-intercepts of the graph of y=fx are -12,0 and 30,0. Of these two x-intercepts, only -12,0 is given as a choice.

Choice B is incorrect and may result from conceptual or calculation errors.

Choice C is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect and may result from conceptual or calculation errors.