**Introduction**

We have learned about angle measures since elementary grades. In Figure 1, we have a circle with center ** A**, and radius length

**1**. Angle

**measures 90 degrees and**

*CAB**intercepting*minor arc

**. This is also the same as saying that arc**

*BC***is**

*BC**subtending*angle

**. We have also learned that the entire rotation about the center of a circle is 360**

*CAB**degrees*.

Another unit of angle measure besides degree is radian. Now, what is radian? How is it related to degree? Continue reading