Geometría proyectiva: Determination of homologous elements in series projective

One of the first problems we must learn to work in projective geometry is the determination of homologous elements. To start the study will use the methodology to be used as usual model-based elements “points”, since it is easier to interpret. Therefore we will consider the determination of homologous elements in series projective:
Given two projective series defined by three pairs of elements (points) counterparts, determine the counterpart of a given point.