Focal length It is proved in a preceding section that if a parabola has its vertex at the origin, and if it opens in the positive direction, then its equation is , where is its focal length. Comparing this with the last equation above shows that the focal length of the parabola in the cone is .
Foc:al length It is proved in a preceding section that if a parabola has its vertex at the orig:in, and if it opens in the positive dir:ection, then its equation is , where .is its f,ocal length. Comparing this with the last equation above shows that the focal length of the parabola in the cone is .