Circles: arcs and sectors

Radius is the distance from the centre to the edge.

Diameter is the distance from edge to edge (going through the centre).

There are some important of a circle that you need to know how to label:

  • Chord: straight line joining two points on the circumference.
  • Arc: part of the circumference.
  • Segment: area enclosed by chord and arc.
  • Sector: area enclosed by two radii and an arc.
  • Tangent: straight line that touches the edge of a circle.

A chord separates the circle into a major arc and minor arc. Also into the major and minor segment.

We need to know how to calculate arc length using this formula:

Arc\quad length\quad =\quad angle\div 360° \times \pi d

Also, know how to calculate the sector area:

The formula to calculate sector area is: Sector\quad area\quad =\quad angle\div 360° \times \pi { r }^{ 2 }

Below are important formulas you need to be aware of: