The formula of radian system: l = π r α/ 180. The method of measuring the angle corresponding to the central angle by the ratio of arc length to radius is called radian system, which is expressed by the symbol rad and pronounced as radian. The central angle of an arc with a long radius is called 1 radian angle.
An arc with an arc length equal to the radius and a central angle of 1 radian. (that is, two rays shoot from the center of the circle to the circumference, forming an arc with an angle opposite to the angle. When the arc length is exactly equal to the radius of the circle, the radian of the included angle between two rays is 1).
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In mathematics and physics, radian is the unit of measurement of angle. It is a unit derived from the international system of units, abbreviated as rad. Definition: an arc whose arc length is equal to the radius and whose central angle is 1 radian. That is, two rays shoot from the center of the circle to the circumference, forming an arc with an angle opposite to the angle. When the arc length is exactly equal to the radius of the circle, the radian of the included angle between two rays is 1.
In junior high school mathematics, we learned the formula of arc length: arc length = nπ r/ 180, where n is the number of angles, that is, the arc length corresponding to the central angle n, but if radians are used, the above formula becomes simple: (note that radians are positive and negative) L = | α| r, that is, the product of the size and radius of α.