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Exit presentation

Parallel and Intersecting Lines

What parallel really means

Planks lie across the two rails. Every plank shows the same gap, the distance between the rails.

Two lines, both marked with the same arrow.
Step 1 of 4
  1. Two lines, both marked with the same arrow.
  2. Measure square across at spot A: 14 steps.
  3. Measure square across at spot B, far away: 14 steps.
  4. Try more spots. Same gap each time. The lines are parallel.

The rule

Lines on a flat page that never meet are called parallel lines. Arrow marks (>) on them show that they are parallel. Parallel lines also keep the same gap all the way along.

Measure square across: at a right angle to the lines. Do not measure on a slant. A slanted measurement is always longer than the square-across gap. So a slant would not compare two spots fairly.

Tap b or c. The lab checks with five gaps.

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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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