In a triangle the sum of the angles is 180

Submitted by Isoscel on Wed, 03/19/2008 - 00:45.

In any triangle the sum the angles is 180.

In triangle ABC:
$\angle ABC + \angle BCA + \angle CAB = 180.$

Proof
Let consider line DE by A parallel to BC
Then $\angle DAC=\angle ACB$ and $\angle EAB=\angle ABC$ but $\angle DAC+\angle CAB +\angle EAB=180$