Matematické Fórum

https://forum.matweb.cz/viewtopic.php?id=44240

Ahoj ↑ Kelly:,

Co sa tyka pojmu direkcna priamka (= riadacia priamka), tento pojem je dolezity v monofokalnej definicii kuzekoseciek ( a tiez vtedy je dolezity pojem extracentrcity a ohniska= foyer). 
O tom viac najdes napr v angl. ci fr. Wikipedii. 
Citujem
« ... one can define a conic section purely in terms of plane geometry: it is the locus of all points P whose distance to a fixed point F (called the focus) is a constant multiple (called the eccentricity e) of the distance from P to a fixed line L (called the directrix). For 0 < e < 1 we obtain an ellipse, for e = 1 a parabola, and for e > 1 a hyperbola. »