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#### plane surfaces

Set of points on a plane that describes an area of space.
#### parts of a circle

Circle: closed plane curve; all its points are the same distance from a fixed point (center).
#### quadrant

Quarter of a circle’s circumference; it corresponds to an arc of 90°.
#### center

Point located at the same distance from every point on the circle’s circumference.
#### arc

Section of a circle between two points on the circle.
#### radius

Line that joins a point on a circle’s circumference to its center; it is one half of the diameter.
#### sector

Surface bounded by two radii and an arc of a circle.
#### diameter

Line that connects two points on a circle’s circumference and passes through its center.
#### semicircle

A half circle that is delimited by its diameter.
#### circumference

Length of a circle that corresponds to the product of its diameter and pi.