ACT Math · Function notation and transformations

What is the range of f(x) = -(x-2)² + 9?

What is the range of f(x)=−(x−2)2+9f(x) = -(x-2)^2 + 9?

Answer and explanation

Answer: A: y ≤ 9

The function −(x−2)2+9-(x-2)^2+9 is a parabola with vertex (2,9)(2,9). The leading coefficient is −1-1, so it opens downward and 99 is the maximum output. Every output is at most 99, so the range is y≤9y\le9, choice A. Choice B (y≥9y\ge9) reverses the inequality, which would hold for a parabola opening upward. Choice C (x≤2x\le2) describes inputs, but the range is about outputs, and the function accepts every real xx anyway. Choice D claims every real number can be an output, but y=10y=10, for example, would require (x−2)2=−1(x-2)^2=-1, which is impossible.

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