Final answer:
When a luminous point is located between two mirrors united at a vertex, the angle formed by the mirrors can vary. In this case, with 11 images formed, the angle is classified as a reflex angle.
Step-by-step explanation:
When a luminous point is located between two flat mirrors united in a vertex, it can give rise to multiple images. The angle formed by the mirrors in this situation can be classified as either an acute angle, a right angle, an obtuse angle, or a reflex angle. The specific angle formed by the mirrors depends on the number of images formed.
If 11 images are formed, the angle between the mirrors would be a reflex angle.
Reflex angles are angles larger than 180 degrees but smaller than 360 degrees. Since the luminous point is between the two mirrors, the multiple reflections result in 11 images, indicating a larger angle of reflection.