Final answer:
A nearsighted man who can only see objects clearly within 20 cm should stand 10 cm away from a mirror to see his reflection clearly while shaving.
Step-by-step explanation:
The question relates to how an individual with myopia (nearsightedness) can view his own image in a mirror while shaving if he cannot see objects clearly beyond 20 cm from his eyes. If a person is nearsighted, it means that they have a shorter distance at which they can see objects clearly without the assistance of corrective lenses. When using a mirror, the distance the person must stand from the mirror is exactly half of the distance they can clearly see. This is due to the fact that the light reflected from the mirror would have to travel back to the eyes, effectively doubling the distance viewed. For a nearsighted man who can only see clearly up to 20 cm, he must stand 10 cm away from the mirror to see his reflection clearly while shaving.