Rn is an analytic model of n-D
A point is a vector (n-tuple) in Rn.
Let P be a point and A a non-zero vector.
A line through P and parallel to A is the set of points
The vector A is called the direction vector of the line.
A point Q is on the line if for some t.
The line is the linear span of A.
Thus, we can write . [See Fig.2.1]