This Demonstration shows the equation of a line in 3D in three different forms: parametric, vector, and Cartesian. You can vary the line—the boxes in the result are pull-down menus. You can also choose to show a grid, which you can move parallel to the -, -, or - plane. As you do this, the color of the line will change where it intersects the grid. By changing the value of the parameter , you can locate a particular point on the line.