**Circle, circle line, circumference**

**A circle** is a shape consisting of a curved line completely surrounding an area.

Every part of the line is the same distance from the centre of the area.

**Circumference is **the distance around a circle.

**Circle Terminology**

**Centre:** the point equidistant from all points on the circle.

**Circumference:** the **length** of one circuit along the circle, or the distance around the circle.

**Diameter**: a line segment whose endpoints lie on the circle and that passes through the centre; or the length of such a line segment. This is the largest distance between any two points on the circle. **d=2r**

**Radius: **a line segment joining the centre of a circle with any single point on the circle itself; or the length of such a segment, which is half (the length of) a diameter. **r = d : 2 **

**Chord:** a line segment whose endpoints lie on the circle, thus dividing a circle into two segments.

**Secant:** an extended chord, a coplanar straight line, intersecting a circle in two points.

**Tangent:** a coplanar straight line that has one single point in common with a circle (“touches the circle at this point”).

**S****ector:** a region bounded by two radii of equal length with a common centre and either of the two possible arcs, determined by this centre and the endpoints of the radii.

**Segment**: a region bounded by a chord and one of the arcs connecting the chord’s endpoints. The length of the chord imposes a lower boundary on the diameter of possible arcs.

**Arc:** any connected part of a circle. Specifying two end points of an arc and a centre allows for two arcs that together make up a full circle.