ANGLES IN TRIANGLES
The angle formed between two adjacent sides of a triangle is called an interior angle. The sum of all of the measures of the interior angles in a triangle is 180∘.
An angle formed between a side of the triangle and an adjacent side extending outward is called an exterior angle. The exterior angle of a triangle is equal to the sum of the two opposite interior angles.
In the above diagram a, b, and c are the interior angles. x, y, and z are the exterior angles