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