文[1]介绍的圆锥曲线的性质确实很优美,但其证明较繁.本人提供一种较为简单的证明.图1先介绍一个引理:(因为后面应用该定理,这里所标字母与原题中一致)如图1,B、C分别为△ADN中AN、DN上的点,设AB,CD交于点M,连结NM并延长交AD于E,则N BBD+N CAC=NMME.证明∵N BBD=S△N BMS△DBM= The nature of the conic curve introduced in [1] is indeed very beautiful, but it proves more complicated. I provide a simpler proof. Figure 1 first introduces a lemma: (Because of the application of the theorem, the letters and originals Consistent in the question) In Figure 1, B, C are the points on AN, DN in △ADN, respectively. Let AB and CD intersect at point M, link NM and extend AD to E, then N BBD+N CAC=NMME. Prove ∵N BBD=S △N BMS △DBM=