Radian
From Wikinfo
The radian is the SI derived unit of angle. It is defined as the angle subtended at the center of a circle by an arc of circumference equal in length to the radius of the circle.
There are 2π (about 6.283185) radians in a complete circle. One radian is equal to 180�/π or approximately 57.29578�.
In calculus, the use of radians leads to the simple identity
- <math>\lim_{h\rightarrow 0}\frac{\sin h}{h}=1</math>
which is the basis of many elegant identities in mathematics.
Conversion of degrees to radians can be carried out using the formula
- <math>radians=\frac{\pi\cdot degrees}{180}</math>
The radian was formerly an SI supplementary unit, but this catagory was abolished from the SI system in 1995.
For measuring solid angles, see steradian.
See also: trigonometry, harmonic analysis
References
- Adapted from the Wikipedia article, "Radian" http://en.wikipedia.org/wiki/Radian, used under the GNU Free Documentation License
