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As we have already dealt with the vertical line test, we will look at the horizontal line test in this section.
A horizontal line test is used on a one-to-one function represented on a graph sheet.
Horizontal line test:
A function is said to be one-to-one if a horizontal line intersects the curve exactly once from any point.
Let us look at the example given below for a better understanding.
Here, the blue curve denotes the one-to-one function. The red line indicates the horizontal line drawn for the line test.
The red horizontal line intersects the blue curve exactly at one point. Hence, it represents a one-to-one function.