Circles and PiArcs Rad

If the central angle is measured in radians rather than degrees, we can use the same equations, but have to replace 360° with :

arc length=2πr×c2π
=r×c
sector area=πr2×c2π
=12r2c

Notice how the equations become much simpler, and π cancels out everywhere. This is because, as you might recall, the definition of radians is basically the length of an arc in a circle with radius 1.

Now let’s see how we can use arcs and sectors to calculate the circumference of the Earth.