According to the exterior angle theorem, what is true for an exterior angle of a triangle?

The correct answer aligns with the exterior angle theorem, which states that the measure of an exterior angle of a triangle is equal to the sum of the measures of the two non-adjacent (opposite) interior angles. This relationship highlights how the exterior angle serves as an "extension" of the triangle, providing a direct correlation between its exterior and the internal angles.

In this context, the exterior angle provides important information about the interior angles, illustrating a key property of triangles that can be leveraged in problem-solving situations.

The other options fail to accurately describe this theorem; they either misinterpret the relationships between the angles of the triangle or state incorrect geometric properties. Understanding this theorem is essential for analyzing triangles and solving related problems effectively.