Euclid index

Euclid Book 1 - Proposition 15
Opposite angles are equal


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To be proved: If two straight lines cut one another, then they make the vertical angles equal to one another.
Corollary: If two straight lines cut one another, then they make the angles at the point of section equal to four right angles.

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There are lines AB and CD which cut one another at the point E.
  
  
  
  
  
  

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