Properties of Circles
What terms related to circles do I need to know?
- Circles have several specific terms that you need to be familiar with:
- A circle's perimeter is called a circumference
- Its line of symmetry is called a diameter
- The line from the centre of the circle to its circumference is called a radius
- The diameter is equal to 2 × the radius
- A portion of the circumference is called an arc
- A portion of the area, contained between two radii and an arc, is called a sector
- A line between two points on the circumference is called a chord
- The area formed between a chord and an arc is called a segment
- A line which intersects the circumference at one point only, is called a tangent
- The ratio
is equal to π (3.14159...)
Examiner Tip
- Always double check if a measurement is the diameter or the radius
- This is a really common error in exams
- Diameter = 2 × Radius
