Final answer:
Without additional context, it's not possible to provide a specific calculation of the reflection of the vector 321 on a plane. However, general properties of reflections in plane mirrors can be discussed, including the lateral inversion of the image and equality of the angles of incidence and reflection.
Step-by-step explanation:
To calculate the reflection of the vector 321 on the plane, we need additional context. However, if we're dealing with images formed by plane mirrors, we can discuss the general nature of reflections in plane mirrors. A reflection in a plane mirror creates an image that is laterally inverted and the same size as the object, but the question as it stands doesn't provide enough information to give a specific calculation or procedure.
To tackle questions about reflections more accurately, we often use the law of reflection which states that the incident ray, the reflected ray, and the normal (perpendicular to the surface) at the point of incidence all lie in the same plane, and the angle of incidence is equal to the angle of reflection. When working with vectors, the vector representing the object can be resolved into components that are perpendicular and parallel to the mirror's surface. The parallel component remains unchanged, while the perpendicular component reverses direction upon reflection.
If we were given a normal vector to the plane and some additional information about how the vector 321 is oriented with respect to the plane, we could use vector mathematics to calculate the reflected vector.