28.

29a. By crossing the X and Y axes at the zero point, the entire

coordinate system is divided into four equal parts, called

QUADRANTS.

These quadrants are numbered with Roman

numerals, beginning with the quadrant to the right of the Y axis

and above the +X axis.

The numerals increase in a

counterclockwise direction (see figure A, below left). Vectors

always start from the point of origin.

Their angle, used to

denote

vector

direction

of

rotation,

is

measured

COUNTERCLOCKWISE starting from the +X axis.

Angles

between 0 and 90 are in the first quadrant (I). Angles between

90 and 180 fall into the second quadrant (II).

The third

quadrant (III) includes angles between 180 and 270.

The

fourth and final quadrant (IV) completes the circle and includes

angles between 270 and 360 (see figure B to the left).

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