In analytic geometry, using the common convention that the horizontal axis represents a variable and the vertical axis represents a variable , a -intercept or vertical intercept is a point where the graph of a function or relation intersects the -axis of the coordinate system.[1] As such, these points satisfy .
If the curve in question is given as the -coordinate of the -intercept is found by calculating . Functions which are undefined at have no -intercept.
If the function is linear and is expressed in slope-intercept form as , the constant term is the -coordinate of the -intercept.[2]
Some 2-dimensional mathematical relationships such as circles, ellipses, and hyperbolas can have more than one -intercept. Because functions associate -values to no more than one -value as part of their definition, they can have at most one -intercept.
Analogously, an -intercept is a point where the graph of a function or relation intersects with the -axis. As such, these points satisfy . The zeros, or roots, of such a function or relation are the -coordinates of these -intercepts.[3]
Functions of the form have at most one -intercept, but may contain multiple -intercepts. The -intercepts of functions, if any exist, are often more difficult to locate than the -intercept, as finding the -intercept involves simply evaluating the function at .
The notion may be extended for 3-dimensional space and higher dimensions, as well as for other coordinate axes, possibly with other names. For example, one may speak of the -intercept of the current–voltage characteristic of, say, a diode. (In electrical engineering, is the symbol used for electric current.)