There are two main ways to measure angles. The first one that you know is called degree angle measure. The new type that we’re learning is called radian angle measure (which is what ”rad” stands for on your calculator).

The circumference of a circle is 2\pi r. So a circle with a radius of 1 has a circumference of 2\pi.


    \[360^\circ = 2\pi  \text{ radians} \hspace{1in} \pi \text{ radians}=180^\circ\]


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To convert from degree to radian \times \frac{\pi}{180}

To convert from radian to degree \times \frac{180}{\pi}