We will go into greater detail on this in the next chapter, this is just so you can be familiar with the two different units of angle measurement.

A radian is a unit of measurement that is determined by the angle formed when the arc length along the unit circle is also 1 unit.

Compare that with one degree:

Given that 1 radian sweeps exactly 1 unit along the circumference of the circle, you might consider asking: how many radians does it take to sweep the full circumference? In that case, you would need to calculate the circumference: \(C = 2\pi r\), but the radius is just 1, so \(C=2\pi\). This means that to sweep the full circumference will take \(2\pi\) radians. You may already know, but it also takes \(360^\circ\) to sweep a full circle, which leads to the relationship that \(2\pi\) radians \(=360^\circ\), or more commonly used: \(\pi = 180^\circ\).

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