初中教科书中指出,三角形的三条中线、角平线、高分别交于一点,其中中线与角平分线的情形很容易证得,唯三条高交于一点较难证明,下面给出一种利用圆证明三角形的三条高交于一点的方法.证明三角形的三条高交于一点.证(1)当ABC为锐角三角形时,如图1.作CE⊥AB于E,BD⊥AC于D,设两垂 In the junior high school textbooks, it is pointed out that the triangle’s three center lines, angle lines, and heights intersect at one point, and the middle line and the angle bisector are easy to prove. Only three high points are more difficult to prove. The following gives a use of circle. Prove that the three triangles are high at one point. Prove that the three highs of the triangle intersect at one point. (1) When ABC is an acute triangle, as shown in Figure 1. For CE⊥AB in E, BD⊥AC in D, set two Hanging