Angle sum in a tringle . Exterior angle

author: Петя
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Българска версия:

§Theorem:

The sum of the angles in a triangle is 180°.

Consequences:

            1. In a triangle only one angle can be obtuse or right.

            2. The sum of acute angles in a right triangle is 90°.

An exterior angle on a triangle is a supplementary angle to some of the angles on the triangle. 

§Each exterior angle for a triangle is equal to the sum of the two unsupplementary angles in the triangle.

§Each exterior angle on a triangle is bigger than every interior and unsupplementary angle from the same triangle.