What do you suppose is the direction of the vector represented by:

(4, 0)^{T}

The vector is parallel to the X axis of the coordinate frame we are using. Often this is horizontal, pointing right. (Or, you might have said that the vector is oriented at 0 degrees.)

A 2D vector that is aligned with a coordinate axis,
as with **(4,0) ^{T}**,
has an orientation
that is easy to see.
It is 0 degrees, 90 degrees,
180 degrees, or 270 degrees.

The orientation of a vector is usually expressed as an angle with the positive x axis of a coordinate frame. There are two ways of doing this:

- The angle is 0
^{o}to 360^{o}measured as a counter-clockwise rotation from the positive x axis. - The angle is 0
^{o}to +180^{o}measured as a counter-clockwise rotation from the positive x axis, or is 0^{o}to -180^{o}measured as a clockwise rotation from the positive x axis,