Jul 24, 2018 · One radian is the angle created by bending the radius length around the arc of a circle. Because a radian is based on an actual part of the circle rather than an arbitrary division, it is a much more natural unit of angle measure for upper level mathematics and will be especially useful when you move on to study calculus.
The blue arc measures 240°. Measurement by arc length : Formula: s = rθ s = arc length r = radius of the circle θ = measure of the central angle in radians. Red arc: r = 2 and θ = 2π/3, so s = 4π/3. Blue arc: r = 2 and θ = 4π/3, so s = 8π/3