## Precalculus (10th Edition)

The radian is the standard unit for measuring angles, used in most mathematical areas. $1$ radian is the central angle belonging to the arc of a circle with the same length as the radius of the circle. $2\pi \text{rad}=360^\circ\\1\text{rad}=\frac{360^\circ}{2\pi}=57.29^\circ$
The radian is the standard unit for measuring angles, used in most mathematical areas. $1$ radian is the central angle belonging to the arc of a circle with the same length as the radius of the circle. $2\pi \text{rad}=360^\circ\\1\text{rad}=\frac{360^\circ}{2\pi}=57.29^\circ$