Properties of Circles (Cambridge International IGCSE Mathematics)

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

Parts of a circle

• The ratio $\frac{\mathrm{circumference}}{\mathrm{diameter}}$ is equal to π(3.14159...)

• Circles have many angle properties and you will need to learn some of them

  • These can be found in the revision note named Circle Theorems

Exam Hint Always double check if a measurement is the diameter or the radius, this is a really common error in exams.

Diameter = 2 × Radius.