adj. (of a number, line, angle, etc.) having an orientation or direction distinguished from an opposite orientation or direction, usually by the use of plus and minus signs. Thus two points A and B determine not one but two directed lines, AB^→ and BA^→, lying in the same position (its direction), but with opposite orientation (its sense); but any two points can be used to distinguish the two directed lines by specifying which precedes the other. In this case,
| BA^→ | = | AB^→ | and BA^→ = -AB^→; thus a line, AB, is not a directed line, as it has only direction and not sense. For example,the directed lines BA^→ and CD^→ have the same length and direction, but opposite sense; regarded as vectors they have resultant zero. Inclination and declination are directed angles with opposite sense, as, for example, are angles XOY and XOZ in the figure.