ABSTRACT
Let us start our excursus in the group theory from studies of transformations of the threedimensional Euclidean space. We consider transformations:
x′ = Rx, (2.1)
leaving a scalar product (x · y) invariant, for which the relation: (x′ · y′) = (x · y) (2.2)
is true. As follows from (2.2), these transformations are carried out through orthogonal matrices
RRT = RTR = I.
