Euclid index

Euclid Book 1 - Proposition 29
Parallel lines makes angles equal


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To be proved: A straight line falling on parallel straight lines makes the alternate angles equal to one another, the exterior angle equal to the interior and opposite angle, and the sum of the interior angles on the same side equal to two right angles.

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There is a line EF crossing parallel lines AB and CD
  
  
  
  
  
  
  
  
  
  
  

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