The formula of focal radius of 1. ellipse
Let M(xo, y0) be an ellipse x2/a2+y2/b2 =1(a >; B>0), r 1 and r2 are the distances between point m and points F 1(-c, 0) and F2(c, 0), then (left focal length) r 1=a+ex0, (right focal length) r2=a -ex0. Derivation: r1/∣ Mn1∣ = R2/∣ Mn2 ∣ = E Available: r1= E ∣ Mn1∣ = E (.
2. The formula of focal radius of hyperbola
The formula of focal radius of point P at the right branch of hyperbola (where F 1 is the left focus and F2 is the right focus) is derived from the second definition, where a is the real semi-axis length, e is the eccentricity and x is the abscissa of point P. |PF2|=ex。 -a and only remember the right branch, the left branch and the right branch are all negative. If the focus is on the Y axis, just remember that the radius of the upper hyperbola passing through the right focus is R = | a-ex | and the radius of the hyperbola passing through the left focus is R = | a+ex |.
3. Formula of focal radius of parabola
Parabola r = x+p/2 0), C(Xo, Yo) is a point on the parabola, and the focal radius |CF|=Xo+p/2.