# Angle Measure in Radian

1.  $\rhd$ Introduction to radians (10:51)This video explains the definition and motivation for radians and the relationship between radians and degrees, including the identities by which we can convert between radians and degrees.
2.  $\rhd$ Radians and degrees (7:12)Sal discusses the general approach to converting between radians and degrees and vice versa.  Describes identities, then converts $30$ degrees to radians — including nice explanation of unit conversion.Also converts $45$ degrees to radians and $-\frac{\pi}{2}$ radians to degrees.
3.  $\rhd$ Converting degrees to radians (7:01)This video shows how to convert the degree measures 150° and -45° to radians.
4.  $\rhd$ Converting radians to degrees (3:19)
Converts $\pi$ and $-\frac{\pi}{3}$ radians to degrees.
5.  $\star$ Converting from radians to degrees and visa versa
Assorted example problems
6.  $\rhd$ Radians and Quandrants (3:51)
This video show how to find the quandrant in which a ray formed by rotation of $\theta$ radians lies.Examples: $\frac{3\pi}{5}$, $\frac{2\pi}{7}$, $3$ radians.