Plane Trigonometry

1. Directed magnitudes. The use of positive and negative numbers is a familiar method of indicating temperatures either above or below a certain fixed temperature, which is taken as the zero of the scale. In the same way, it is convenient to use positive and negative numbers to designate the measures of other magnitudes, the values of which may fall on either side of a certain fixed value, taken as a point of departure. For example, northern latitude may be designated as positive, southern latitude as negative; eastern longitude as positive, western longitude as negative; a credit balance as positive, a debit balance as negative; altitude above sea level as positive, altitude below sea level as negative, etc.2. Points on a line. Directed lines. A simple graphical representation of such magnitudes is obtained by means of a straight line, called the axis, upon which are indicated a fixed point, called the origin, a unit distance and a positive direction.O (Origin) 1 Table of Contents 1 D