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Parallel and Intersecting Lines

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Look at a railway track. Do the two rails ever meet?

One line across two makes eight angles to learn.

Part I, Chapter 5 of your book is Parallel and Intersecting Lines.

What you will learn

  • Two straight lines meet once, or never meet at all.
  • Parallel lines never meet, and keep the same gap.
  • A crossing makes four angles. Two pairs face each other and match.
  • Angles on a line add to 180°. All round a point, 360°.
  • A line across two lines makes eight angles, with three named pairs.
  • Those pairs match only when the two lines are parallel.
  • You can walk from one known angle to another. Each step uses one named fact.
  • Lines at a right angle are perpendicular. A small square marks the corner.
  • Two lines perpendicular to a third line are parallel. You can draw them with a set square or by folding paper.
  • A bend between two parallels is the sum of two marked angles. Both ends lie on one side.

Quick catch-up

These help.

  • What is an angle? (Lines and Angles). The turn between two rays with one shared start.
  • Measuring an angle (Lines and Angles). A full turn is 360°. A protractor measures an angle.
  • A square corner (Playing with Constructions). Measure a square corner. Do not guess it.

Jump to lesson

This track

  1. 0 Start here
  2. 1 Cross once, or never cross
  3. 2 What parallel really means
  4. 3 The four angles at a crossing
  5. 4 Angles that fill a straight line
  6. 5 One line laid across two
  7. 6 Only when the lines are parallel
  8. 7 Finding an angle nobody measured
  9. 8 Square corners: perpendicular lines
  10. 9 Parallels from square corners
  11. 10 A bend between two parallels
  12. 11 Checkpoint: square corners and bends
  13. 12 The big picture
  14. 13 Track quiz

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