The connecting line between any point m on the conic and the focus of the conic is called the focal radius of the conic. The distance from a point to the focus on a conic curve is not a fixed value. Focus radius: the chord diameter of the line connecting any point on the curve with the focus, focus chord, passing through a focus. A chord (except a circle) that passes through the focus and is perpendicular to the axis.

Extended data:

Let M(m, n) be an ellipse x2/a2+y2/B2 =1(a > b >; 0), r 1 and r2 are points m and f, respectively. (-c，0)，F？ The distance of (c, 0), then (left focal radius) r? =a+em, (right focal radius) r? =a -em, where e is eccentricity.

Parabolic y? = 2px(p & gt； 0)，C(x？ ，y？ ) is a point on a parabola, and the focal radius |CF|=x? +p/2 .

When the axis of symmetry is X, the right end of the equation is 2px and the left end of the equation is y^2；; ; When the symmetry axis is the Y axis, the right end of the equation is 2py and the left end of the equation is x 2.

When the opening direction is the same as the positive semi-axis of X axis (or Y axis), the focus is on the positive semi-axis of X axis (Y axis), and the right end of the equation takes a positive sign; When the opening direction is the same as the negative semi-axis of X (or Y), the focus is on the negative semi-axis of X (or Y), and the right end of the equation takes a negative sign.

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