Explained: How to Use Horizontal Line Test to Solve Questions

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The horizontal line test is a method that is used to determine whether a function is one to one or not. A one-to-one function is also known as an injective function.

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A function is said to be one to one if, for every y value of the function, there is a unique value of x. If we know the graph of a function, place a horizontal line across the graph.

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If the horizontal line crosses the graph in one place, then the function is one to one because there is only one value of x for each value of y.

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If the horizontal line crosses the graph more than two points, then for every value of y, there are many values of x, so the function is not one-to-one.

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If the horizontal line cuts the graph at one point, the function is one to one. Thus the function y = 2x + 3 is one to one function.

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Draw a horizontal line across the graph. The horizontal line cuts the graph at two points. Thus the function is not one to one, as there are 2 values of x for one value of y.

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