读了贵刊2005年第4期的《探讨抛物线切线的若干性质》(徐永忠)后,颇有收获,结合本人的教学经验,认为可对该文中的性质4、性质5进行更进一步的探讨.性质4过抛物线的准线上任一点所作抛物线的两条切线必互相垂直.性质4·1过抛物线上不同的两点分别作抛物线的切线,若两切线垂直,则 After reading Your Number 4, 2005, “Some Properties of Parabola Tangent” (Xu Yongzhong), I learned quite a bit from my teaching experience that I could further explore the nature 4 and nature 5 of this article . Properties 4 Parabola on the quasi-line at any point made by the two tangents of the parabola will be perpendicular to each other. Nature 4.1 Parabola on the different two points were parabolic tangents, if the two tangent perpendicular, then