a circle is a shape consisting of all points on a plane that are at a given distance from a given point
the given distance the radius and the given point is the center
terminology
annulus
a ring shaped object, the region bounded by two concentric circles
arc
any connected part of a circle. specifying two points
center
the point equidistant from all points on the circle. also called the origin of the circle
chord
a line segment whose endpoints lie on the circle
circumference
the length of one circuit along the circle
diameter
a line segment whose endpoints lie on the circle and passes through the center
the length of this line segment is also called the diameter
radius
a line segment joining the center with any point on the circle
the length of this line segment is also called the radius
sector
a region bounded by two radii with a common center and one of the two possible arcs
segment
a region bounded by a chord and one of the two possible arcs connecting the chord’s endpoints
secant
a chord but is a line instead of a line segment
tangent
a line that only has one point in common with the circle
figure: diagram of a circle, showing radius (R), diameter (D), origin (O) and circumference (C)
figure: diagram of a circle showing chord, segment, radius, diameter and tangent
