This applet can be used to determine whether one relation is a function or not by using the Vertical Line Test.
The Vertical Line Test says that if some vertilcal line meets the graph in more than one point then the relation is not a function.
In the input box enter a polynomial equation of x and y in the form "polynomial = number". For example, to graph y = x2, enter y - x2 = 0
Drag the slider to use the vertical line test.
Irina Boyadzhiev, 25 September 2013, Created with GeoGebra