If we draw two straight lines that cross at the centre of a circle, the angle is that part of the circumference (an arc) between the two lines, measured in units of degrees or radians.

A complete circle is defined to contain 2π radians or 360 degrees.

Angles are often indicated with the notation $ \angle AOB $, which indicates the angle between the line segments OA and OB that meet at the point O.

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