IN MATH: 1. n. a way of testing a graphed function to determine if it is 1-to-1, uses each y-value at most once, has the possiblility of having an inverse function. EX. The graph of y=x² fails the horizontal line test because one or more horizontal lines pass through the curve simultaneously. The line through (-2,4) and (2,4), for example.

IN ENGLISH: 1. as defined above.

APPLICATION: See list 300.

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