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Arc of a Circle

A connected section of the circumference of a circle.

Arcs are measured in two ways: as the measure of the central angle, or as the length of the arc itself.

 Measurement by central angle (degrees) The red arc (minor arc) measures 120°. The blue arc (major arc) measures 240°. Measurement by arc length (radians) 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