Well.. You seem to have forgotten to add the coordinates...
Anyway, the line is represented by the function f(x) = 3x .
Any point which follows the form (x,3x) will be on the line
for example (-3,-9) ; (-2,-6) ; (-1,-3) ; (0,0) ; (0.333333,1) ; (1, 3) ; (2,6) ; (3,9) ; and so on....
