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.

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