The graph of which function is decreasing over the interval (–4, ∞)?

f(x) = (x + 4)2 + 4
f(x) = –(x + 4)2 + 4
f(x) = (x – 4)2 – 4
f(x) = –(x – 4)2 – 4

f(x) = (x + 4)² + 4 and f(x) = –(x – 4)² – 4 - don't intersect with the axis X. Their discriminant is less than 0. 

f(x) = (x + 4)² + 4 is located in the 1st quarter of the coordinate space.
f(x) = –(x – 4)² – 4 is located in the 4th quarter of the coordinate space.

f(x) = (x - 4)² - 4 intersects with the axis X in points (2,0) and (6,0), with the axis Y in point (0,12). Parabola branches are directed upwards that's why function is decreasing over the interval (–∞, 4).

f(x) = –(x + 4)² + 4 intersects with the axis X in points (-2,0) and (-6,0). Parabola branches are directed downwards that's why function is decreasing over the interval (–4, ∞).

The correct answer is f(x) = –(x + 4)2 + 4 or B :)

returning points to main account

explanation:

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