Editing Angle (section)

===Related quantities===
For an angular unit, it is definitional that the [[angle addition postulate]] holds. Some quantities related to angles where the angle addition postulate does not hold include:
* The ''[[slope]]'' or ''gradient'' is equal to the [[tangent (trigonometric function)|tangent]] of the angle; a gradient is often expressed as a percentage. For very small values (less than 5%), the slope of a line is approximately the measure in radians of its angle with the horizontal direction.
* The ''[[spread (rational trigonometry)|spread]]'' between two lines is defined in [[rational geometry]] as the square of the sine of the angle between the lines. As the sine of an angle and the sine of its supplementary angle are the same, any angle of rotation that maps one of the lines into the other leads to the same value for the spread between the lines.
* Although done rarely, one can report the direct results of [[trigonometric functions]], such as the [[sine]] of the angle.