The triangle angle sum theorem tells us that, given a triangle in flat Euclidean geometry, the sum of the measures of the interior angles is 180 degrees. But our problem doesn’t give us a triangle.

The sum of interior angles in a triangle is 180˚. In an equilateral triangle, all three angles are equal to 60˚. To find the missing angles in an equilateral triangle, ...

The angle sum of a triangle is 180 degrees. That means all triangles, no matter how differently formed, will have angles that add up to 180 degrees. These angles all add up to equal 180 degrees.