Answer:
When you plot the graph of either, it passes both the horizontal and vertical line tests.
Step-by-step explanation:
A function will pass the vertical line test. This is what make a relation a function. It will have an inverse function if it also passes the horizontal line test. (The inverse function is the reflection of the function across the line y=x.)
Of course, the domain of one is the range of the other, and vice versa.
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The vertical line test passes if no vertical line intersects the graph of the relation in more than one point. The horizontal line test is similar: no horizontal line can intersect the graph in more than one point.
