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The radian, denoted by the symbol rad, is the unit of angle in the International System of Units (SI) and is the standard unit of angular measure used in many areas of mathematics. It is defined such that one radian is the angle subtended at the centre of a circle by an arc that is equal in length to the radius. [2]
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Learn what radians are, how to convert them to degrees and vice versa, and why they are useful in mathematics. See diagrams, formulas and examples of radians in geometry and trigonometry.
Learn the definition and motivation for radians, a unit of angle measurement, and how they relate to degrees. Watch Sal Khan explain the concept with examples, diagrams and questions.
- 11 min
- Sal Khan
- This is a question that bothered me for quite a few years while taking college physics and astronomy and I wish I would have learned this sooner. A...
- I think it's because Sal has a sense of fun, and was playing with the word "radiuses". Foolishly, perhaps, thinking that others might share his sen...
- When you click where to type in your answer it comes up with little buttons underneath that you can click on and one of them is the pi symbol
- Historical convention. π has been used historically much more than 𝜏, so there are few people in the world that actually understand if you start u...
- No, nor is there any need. Remember that an angle in radians is just the ratio of that arclength to the radius, so the units cancel out. To avoid c...
- Radians are used to measure angles. You might be more used to measuring angles with degrees, in which case it should help to think of radians as a...
- The degree symbol was first used in the 1500s, and it seems to have originated as a superscript zero. Sort of like the ' and " used for for feet an...
Learn what a radian is, how to convert it to degrees and vice versa, and how to use it in trigonometry and calculus. Find out the common angles in radians and degrees and their formulas.
Learn how to use radians to measure angles and determine the quadrant of a point on the unit circle. Watch a video example and read the transcript and comments.
- 4 min
Learn how to convert between radians and degrees and vice versa with examples and explanations. See questions and answers from other learners about angles, pi, and notation.
- 7 min
- Sal Khan
People also ask
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