An obtuse triangle will have one and only one obtuse angle.
The other two angles are acute angles.
The sum of the two angles other than the obtuse angle is less than 90º.
The side opposite to the obtuse angle is the longest side of the triangle.
The points of concurrency, the Circumcenter and the Orthocenter lie outside of an obtuse triangle, while Centroid and Incenter lie inside the triangle.
