The coefficient

*k*of proportionality between the lengths of the image of an initial geometric figure and the corresponding lengths of the initial figure by a similarity.- To determine the ratio of similarity, all that is required is two points
*A*and*B*and their images,*A′*

and*B′*.

Therefore, the ratio of similarity is:*k*= \(\dfrac{\textrm{m}\overline{\textrm{A’B’}}}{\textrm{m}\overline{\textrm{AB}}}\).