This GeoGebra applet can be used to introduce functions and to discuss whether or not a relation is a function. [br]Initial values for x and y are entered in the blue and green columns to the right. They can be changed to different values. [br][*]Press repeatedly the red button Point in the upper left corner. This will plot the points (x,y) from the table.[br][*]Select the checkbox to display the vertical segments connecting the corresponding points.