To draw a line you just need to sample two of its points, and connect them.
Since the x and y coordinates have to be the same, all points with coordinates like [tex] (k,k) [/tex] will be on the line.
For example, [tex] (0,0),\ (1,1),\ (13,13),\ (-40,-40) [/tex] are all points on the line.
So, you can pick two easy points to draw, like (0,0) and (1,1), and connect them with a line.
That will be the line with equation [tex] y =x [/tex]
To check the result, you should get the bisector of the first and third quadrant.
