Final answer:
The image formed by the lens is also the image seen when looking in the mirror.
Step-by-step explanation:
To determine the location of the image when looking in the mirror, we need to consider the ray diagrams and the properties of light. In this case, the lamp is placed 40 cm in front of a converging lens with a focal length of 20 cm. Behind the lens, there is a plane mirror located 15 cm away.
When light rays pass through the lens, they converge at the focal point. Since the object is located in front of the lens, the rays will converge to form a real image on the opposite side of the lens.
However, when the rays hit the plane mirror, they are reflected in such a way that they continue to converge to the same point. Therefore, the image formed by the lens is also the image seen when looking in the mirror.