The plane is divided into two parts by an angle into two flat angles. Flat corners with common sides are called
extra . A measure of a flat angle that is part of a half-plane is called a degree measure of the angle with the same sides. The measure of a flat angle that contains a half-plane is called 360 ° α, where α is the degree measure of the additional flat angle.
A central angle in a circle is a flat angle with a vertex at its center. The part of a circle located inside a flat angle is called the
arc of a circle .
The degree measure of a circular arc is the degree measure of the corresponding central angle.
An angle is called
inscribed in a circle if the vertex of the angle lies on the circle, and the sides of the angle intersect this circle. ∠ ABC inscribed in a circle.
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