Prove that the sum of the measures of the interior angles of a triangle is 180°

Question

anonymous · Answer

It's a postulate

anonymous · Answer

Proof 1

Construct a line through B parallel to AC. Angle DBA is equal to CAB because they are a pair of alternate interior angle. The same reasoning goes with the alternate interior angles EBC and ACB.

alternate interior angles

myininaya · Answer

You could take a triangle. Do some rotations,reflections, and/or translations to lay the 3 angles on one line to show the sum of the angles equal 180 degrees.

myininaya · Answer

That is the most elementary proof you will ever get.

myininaya · Answer

That I can think of...lol.