A line is entered as a linear equation in x and y or in parametric form. In both cases previously defined variables (numbers, points, vectors) can be used. The line's name has to be entered at the beginning of the input followed by a colon.
| equation | parametric form | |
| line g | g : 3x + 4y = 2 | g : X = (-5, 5) + t (4, -3) |
Let be k=2 and d=-1 for example. Then we can define a line g by entering the equation g : y = k x + d.
The two coordinate axes are available in commands using the names xAxis and yAxis. For example, the command Perpendicular[A, xAxis] constructs the perpendicular line to the x-axis through a point A.