Congruences of ruled quadrics with two double focal surfaces
In three-dimensional projective space P3 two-parametric families (congruences) V2 of rouled non-degenerates quadrics Q are investigated. It is proved that such congruences exist and with arbitrariness of five arbitraries functions of two arguments are defined. Using computer-program [1] four subclasses of such congruences are considered. If points A1 and A2 of intersection of lines A0A1, A3A1 and A0A2, A3A2 of quadric QV are also focal points than (A0) and (A3) are double focal surfaces it is istablished.