Click on the image to see just the image, 
IN MATH: 1. n, an angle measure (symbol rad may be used, though no symbol is needed).
IN MATH: 2. n. 1 radian is a constant, like pi, and e, and the square root of 2. It is about 57.3, but is irrational like the other constants listed here. It divides the circle into nice, simple, pieces. Angle measures need not be written in degrees, but may be written as numbers. See: Radians & Sectors Using radianSector.gsp: video, Sketchpad, worksheet, answers key words: angle, circle formulas from middle school, special angles, degree measures, radians, radian measures, arc, arc length, sector, angular speed See: Angle Measure, a history of angle measurement, web page, video, page pdf file key words  ancient counting and communication of numbers, Egyptian mathematics, Sumerian/Babylonian mathematics, construction of a hexagon, Roman/Greek mathematics, pi, radians, graph papers, other tools sfor teaching radians 





5.1 Circle's arcs and sectors Radians make circle computation and these formulas MUCH easier and clearer. For the full story, see Arc Formulas and Rational, and Sector Formulas and Rational. Click on the image below to see an enlargement of the formulas that are used here. 

IN ENGLISH: 1. as defined above.
APPLICATION: See list 330.
This is a page from the dictionary MATH SPOKEN HERE!, published in 1995 by MATHEMATICAL CONCEPTS, inc., ISBN: 0962359351.
www.mathnstuff.com/math/spoken/here/1words/r/r1.htm 