Let [b]d[/b] be the vector whose direction is parallel to the line.[br]Let (x[sub]0[/sub],y[sub]0[/sub]) be a fixed point on the line.[br]For some parameter t, the vector [b]td [/b]points to any point (x,y) on the line.[br]If we can describe any point on a line, we can describe the line itself.