To test if a graph is also a function, we can use the vertical line test. For the inverse function, we use the horizontal line test. This is part of the Prelim Maths Extension 1 Syllabus from the topic Functions: Further, Work with Functions, specifically focusing on testing for a function. Here we will learn to, using the fact that this reflection exchanges horizontal and vertical lines, recognise that the horizontal line test can be used to determine whether the inverse relation of a function is still a function.
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