Question

Which graph shows a function whose inverse is also a function?

On a coordinate plane, 2 curves are shown. f (x) is a curve that starts at (0, 0) and opens down and to the right in quadrant 1. The curve goes through (4, 2). The inverse of f (x) starts at (0, 0) and curves up sharply and opens to the left in quadrant 1. The curve goes through (2, 4).

On a coordinate plane, 2 parabolas are shown. f (x) opens up and goes through (negative 2, 5), has a vertex at (0, negative 2), and goes through (2, 5). The inverse of f (x) opens right and goes through (5, 2), has a vertex at (negative 2, 0), and goes through (5, negative 2).

On a coordinate plane, two v-shaped graphs are shown. f (x) opens down and goes through (0, negative 3), has a vertex at (1, 3), and goes through (2, negative 3). The inverse of f (x) opens to the left and goes through (negative 3, 2), has a vertex at (3, 1), and goes through (negative 3, 0).

On a coordinate plane, two curved graphs are shown. f (x) sharply increases from (negative 1, negative 4) to (0, 2) and then changes directions and curves down to (1, 1). At (1, 1) the curve changes directions and curves sharply upwards. The inverse of f (x) goes through (negative 4, negative 1) and gradually curves up to (2, 0). At (2, 0) the curve changes directions sharply and goes toward (1, 1). At (1, 1), the curve again sharply changes directions and goes toward (3, 1).

Answer 1

The first graph.

Reason: that f is one-to-one (monotonic in the pictured domain), so it passes the horizontal-line test and its inverse is a function. The parabola (option 2) and the V-shape (option 3) fail the horizontal-line test, and the fourth graph is not one-to-one because it changes direction, so their inverses are not functions.