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I'm Up and Down, and Round and Round

Checkpoint: parts, chords and the doubling

Five ideas so far, one question on each. Retry any time.

Two radii and one arc cut off a piece of a circle. What is it called?

A circle has radius 15 cm and a chord 24 cm long. How far is that chord from the centre?

Two chords sit 6 cm and 9 cm from a circle's centre. Which is true?

An arc makes an angle of 130° at the centre. What angle does it make at the rim?

P and Q both sit on chord AB's major arc. What can you say about angles APB and AQB?

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This track

  1. 0 Start here
  2. 1 Four names for four parts of a circle
  3. 2 The line from the centre that cuts a chord in half
  4. 3 Same distance, same length — and further out is shorter
  5. 4 An arc makes twice the angle at the centre that it makes at the edge
  6. 5 Every point on one arc sees the chord the same way
  7. 6 Checkpoint: parts, chords and the doubling
  8. 7 A corner standing on a diameter is a right angle
  9. 8 Four corners on one circle, and the pairs that total 180°
  10. 9 Testing whether four points really share one circle
  11. 10 Three points give one circle, and the triangle shows where its centre is
  12. 11 Checkpoint: diameters, cyclic shapes and finding a centre
  13. 12 Many circles fit through two points
  14. 13 A circle looks the same when turned
  15. 14 Equal angles at the centre give equal chords
  16. 15 Equal angles on one side put four points on a circle
  17. 16 The big picture
  18. 17 Track quiz

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