29a. By crossing the X and Y axes at the zero point, the entire
coordinate system is divided into four equal parts, called
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
COUNTERCLOCKWISE starting from the +X axis.
between 0 and 90 are in the first quadrant (I). Angles between
90 and 180 fall into the second quadrant (II).
quadrant (III) includes angles between 180 and 270.
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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