圆锥曲线有很多性质,最近笔者研究发现,椭圆切线有如下两个有趣性质:性质1椭圆的两条平行切线与第三条切线相交,则(1)第三条切线上的两切线段之积等于其切点处的两焦半径之积;(2)两平行切线上的两切线段之积等于其切点处的两焦半径之积.如图1,椭圆的两平行切线l1,l2分别与第三 The conic curve has many properties. Recently, the author found that the elliptic tangent has the following two interesting properties: the two parallel tangents of the property 1 ellipse intersect with the third tangent, then (1) the product of the two tangent sections on the third tangent It is equal to the product of two focal radii at its tangent; (2) The product of two tangent segments on two parallel tangents is equal to the product of two focal radii at its tangent point. As shown in Fig. 1, two parallel tangents l1, l2 of ellipse are respectively With third