Answer:
When the incident ray passes through the focal point
Step-by-step explanation:
A concave mirror has an inward curved surface that reflects the light making it converge at a focal point. It is characterized by the fact that, unlike convex mirrors, concave mirrors show images of different shapes depending on the distance between the object and the mirror.
When the object is at the same focal point, the reflected rays are parallel and never cross, so no image is formed, or in other words, it is reflected parallel to the main axis.