Look at each function (one at a time would be best). Use the slider to move the point on the graph. Notice that each graph has places where there seem to be gaps or jumps. These gaps and jumps are places where the graph is undefined (the y-value is not a real number at that x-value). The DOMAIN of a function is the set of all x-values that produce real number answers.
Kelly Harms, Created with GeoGebra Upgraded by S.H.Lapinski