La parábola se define como el lugar geométrico de los puntos del plano que equidistan de un punto  llamado foco y de una recta denominada directriz.[br][br]En una recta r (directriz) marcamos un punto A y en la recta perpendicular a la anterior por el punto A, marcamos un punto F que será el foco de la parábola. En la directriz situamos un punto P y trazamos la[br]perpendicular a la directriz. [br][br]A continuación, trazamos la mediatriz del segmento PF para obtener el punto P1, intersección de la mediatriz con la perpendicular anterior.[br][br][img 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punto P1 cumple la condición para pertenecer a la parábola, ya que la distancia a la recta r (directriz) es igual a la distancia al foco F.[br][br]Por tanto, la parábola se obtendrá como lugar geométrico del punto P1 cuando el punto P recorre la recta r.[br]