This lesson focuses on correspondence between the information that is necessary to give the equation of a line and the geometric information needed to graph a line The parametric form of a line is motivated first using an example in two dimensions, then generalizing to an example in three dimensions. The description for how the parametric form of a line is animated in three dimensional example presented in this lesson. The playground on lines allows the user to move either of the two points used to define a line and the graph and equations are updated dynamically.