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Constructions and Tilings

The corners must add to 360°

Floor tiles meet at points. Why do some shapes leave gaps?

120° times 3 fills the point. 108° times 3 falls 36° short.

A full turn is 360°

Some shapes leave gaps because their corners do not add to 360°. Take a point where tiles meet. Each tile there has a corner at that point. The corners must fill the full turn round that point. So they must add to 360°. Not more and not less.

Three corners of 120° fill it. 120 × 3 = 360. Three corners of 108° do not. 108 × 3 = 324, which is 36° short.

What can meet at one point
Corners meetingTotalFits?
Six 60° corners360°Yes
Four 90° corners360°Yes
Three 120° corners360°Yes
Three 108° corners324°No. 36° short
Four 108° corners432°No. 72° too much

Add corners round the point. Try to reach 360°.

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This track

  1. 0 Start here
  2. 1 Copy a corner, no protractor
  3. 2 The line fair to both ends
  4. 3 Split a corner in two
  5. 4 A parallel through a point
  6. 5 Three lengths, one triangle
  7. 6 Two sides, the angle between
  8. 7 Covering a floor with no gaps
  9. 8 The corners must add to 360°
  10. 9 A square line from a point
  11. 10 60°, 30° and 15° with a compass
  12. 11 A hexagon from a circle
  13. 12 The tangram
  14. 13 Tiling the whole floor
  15. 14 Checkpoint: perpendiculars, 60°, hexagons and floors
  16. 15 The big picture
  17. 16 Track quiz

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