In which configuration is the circumcenter located in an obtuse triangle?

In an obtuse triangle, the circumcenter is found outside of the triangle. The circumcenter is the point where the perpendicular bisectors of the sides of the triangle intersect, and it serves as the center of the circumcircle, which passes through all the vertices of the triangle.

For an obtuse triangle, one of the angles is greater than 90 degrees, which causes the perpendicular bisectors of the sides related to the obtuse angle to intersect at a point situated outside the triangle itself. This occurs because the position of the circumcenter is influenced by the angles of the triangle; as an angle becomes obtuse, the location of the circumcenter shifts outside the triangle to accommodate the larger angle.

In contrast, for acute triangles, the circumcenter is located inside the triangle, while in right triangles, it lies on the hypotenuse. Therefore, the unique characteristic of the obtuse triangle is that its circumcenter is positioned externally, confirming that option A is the correct choice.