Euclid Book 1 - Proposition 15
Opposite angles are equal

Index --- introduction --- definitions --- axioms and postulates --- propositions --- other

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.

Step through proof by clicking on Next line:

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

Previous proposition - Next proposition

© Jo Edkins 2010 - Return to Euclid index