The angles inside a triangle are called interior angles. The diagram below shows the interior and exterior angles of a triangle. The three interior angles in a triangle will always add up to 180°. At each corner the exterior and interior angles are on a straight line, so at each corner these two angles add up to 180°.
The (interior) angles of a triangle always add up to 180 degrees. To find the exterior angles of a triangle, subtract the interior triangle from 360 degrees.
The total degrees of any polygon is (n-2)×180 (n is the number of angles). 3-2 is 1 and 1 times 180 is 180. Therefore, the angles of a triangle always add up to 180 degrees.
