Practice Exam

Question 9 • Mathematics I

Which graph represents a function?

Answer

Image with description On a coordinate plane, a curved line crosses the y-axis at (0, 1.5), the x-axis at (negative 2, 0), and the y-axis at (0, negative 1.5).

Image with description On a coordinate plane, a line with 2 angles crosses the x-axis at (negative .5, 0), the y-axis at (0, 1), turns at (1, 3), crosses the x-axis at (1, 0), turns at (1, negative 2), and crosses the x-axis at (2, 0).

Image with description On a coordinate plane, a line enters the plane at point (negative 5, 4), makes a 90-degree turn at (negative 1, 0), and leaves the plane at point (negative 5, negative 4).

Image with description On a coordinate plane, a line with an s curve enters the plane at point (negative 3.75, 5), crosses the x-axis at (negative .75, 0), the y-axis at (0, 0), leaves x-axis at (.75, 0), and exits the plane at point (3.75, negative 5).

Explanation

A graph represents a function if every vertical line intersects it at most once, so each x-value has only one y-value. In choice D, the S-shaped curve moves across the plane without doubling back horizontally, so it passes the vertical-line test. The other graphs have at least one x-value paired with multiple y-values, such as x = 0 in A and x = 1 in B.

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