27a. Vectors must be used with a known reference. By using coordinate lines, we can
establish a known reference for vectors.
A complete coordinate system consists of two
perpendicular lines that cross each other at a point called the zero point. (Refer to figure A
below.) The zero point is also called the POINT OF ORIGIN. All vectors will start from this
point. The horizontal and vertical lines that pass through this point of origin are known as the
"X" and "Y" AXES. Both the X and Y axes are divided at the zero point into positive and
negative values. The horizontal line is the X axis. all values to the RIGHT of the zero point are
POSITIVE (+); all values to the LEFT are NEGATIVE (-). The vertical line is the Y axis. All
values above the zero point are positive, while values below are negative. Figure B below
shows the labeling of the two axes in the coordinate system.