Geometry & measures · Circles, arcs & sectors
Chapter 1 · 3
The idea
Parts of a circle
The names of the parts of a circle and how to tell them apart: centre, radius, diameter and circumference; chords, arcs and tangents; sectors and segments, minor and major. Why the diameter is twice the radius, and how two radii make an isosceles triangle.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Geometry & measures · Circles, arcs & sectors
Parts of a circle
The names of the parts of a circle and how to tell them apart: centre, radius, diameter and circumference; chords, arcs and tangents; sectors and segments, minor and major. Why the diameter is twice the radius, and how two radii make an isosceles triangle.
Why it works
The centre and the radius
A pizza menu says "large: cm". What has been measured? To answer that, you need the names of the parts of a circle.Every point on the edge of a circle is the same distance from one middle point. That middle point is the centre, usually labelled . A straight line from the centre to the edge is a radius, and the plural of radius is radii. Every radius of a circle has the same length. That is what makes the pizza round.
Keep reading — free
The rest of the explanation, plus 4 worked examples you step through move by move.
Start freeTakes a minute — no card.