plane surfaces![click to hear](/images/speaker.jpg)
Set of points on a plane that describes an area of space.
parts of a circle ![click to hear](/images/speaker.jpg)
Circle: closed plane curve; all its points are the same distance from a fixed point (center).
quadrant ![click to hear](/images/speaker.jpg)
Quarter of a circle’s circumference; it corresponds to an arc of 90°.
center ![click to hear](/images/speaker.jpg)
Point located at the same distance from every point on the circle’s circumference.
arc ![click to hear](/images/speaker.jpg)
Section of a circle between two points on the circle.
radius ![click to hear](/images/speaker.jpg)
Line that joins a point on a circle’s circumference to its center; it is one half of the diameter.
sector ![click to hear](/images/speaker.jpg)
Surface bounded by two radii and an arc of a circle.
diameter ![click to hear](/images/speaker.jpg)
Line that connects two points on a circle’s circumference and passes through its center.
semicircle ![click to hear](/images/speaker.jpg)
A half circle that is delimited by its diameter.
circumference ![click to hear](/images/speaker.jpg)
Length of a circle that corresponds to the product of its diameter and pi.