Circles: radius, diameter and circumference
Centre, radius, diameter, circumference, chord, arc, sector and segment of a circle. Read one part at a time and tap “I know this”. Then test yourself in the quiz.
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The parts of a circle
- Centre: the point in the middle.
- Radius (r): centre to the edge.
- Diameter (d): right across through the centre; d = 2r.
- Circumference: the distance around; C = π × d (π ≈ 3,14).
- Chord: a straight line joining two points on the circle. The diameter is the longest chord.
- Arc: part of the circumference.
- Sector: the “slice of pizza” between two radii and an arc.
- Segment: the part between a chord and an arc.
r = 5 cm → d = 10 cm → C ≈ 3,14 × 10 = 31,4 cm.
Remember this and test yourself
- Radius: centre to edge.
- Diameter = 2 × radius.
- Circumference = π × diameter.
- π ≈ 3,14.
- Chord: line between two points on the circle; arc: part of the circumference.
- Sector: between two radii; segment: between a chord and an arc.
Write these points in your book. Read them again the night before the test.
Diameter goes right through the middle; radius goes from the middle to the edge.
Important words
First say the answer yourself, then turn the card over.
Match column A to column B
Tap a word in column A, then its meaning in column B. You can also start in column B.
True or false?
Read the question and the answer. Is the answer right? Tap True or False.
Now the real quiz!
The quiz has many more questions on this topic. Every question shows straight away whether you are right and explains why.
Take the quiz: Circles: radius, diameter and circumference- Let your child work the examples on paper and explain them to you.
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Follows CAPS for Grade 7 Mathematics. Always check your teacher’s notes and textbook too.