Euclid index

Euclid Book 1 - Proposition 32
Angles of a triangle add up to 180°

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

To be proved: In any triangle, if one of the sides is produced, then the exterior angle equals the sum of the two interior and opposite angles, and the sum of the three interior angles of the triangle equals two right angles.

Step through proof by clicking on Next line:

There is a triangle ABC. 

Previous proposition - Next proposition