In mathematics, the vertical line test is a visual way to determine if a

curve In mathematics, a curve (also called a curved line in older texts) is an object similar to a line (geometry), line, but that does not have to be Linearity, straight. Intuitively, a curve may be thought of as the trace left by a moving point (ge ...

is a

graph of a function In mathematics, the graph of a function f is the set of ordered pairs (x, y), where f(x) = y. In the common case where x and f(x) are real numbers, these pairs are Cartesian coordinates of points in two-dimensional space and thus form a subset ...

or not. A function can only have one output, ''y'', for each unique input, ''x''. If a vertical line intersects a curve on an ''xy''-plane more than once then for one value of ''x'' the curve has more than one value of ''y'', and so, the curve does not represent a function. If all vertical lines intersect a curve at most once then the curve represents a function.

Notes

{{Reflist Functions and mappings

See also

Notes