在平几中,证明“三线共点”的问题,是不乏其例的;证明“三线共点”的方法亦多.这里介绍一种比较有效的证明方法.先看图1,已知点 P 在△ABC 的边 BC、CA、AB(或其所在直线)上的射影是 D、E、F,连结 In the case of peace, there are no shortages of examples to prove the problem of “three lines of common points”; there are also many ways to prove “three lines of common points.” Here is a more effective proof method. Look at Figure 1, known point P The projections on the sides BC, CA, AB (or their straight line) of △ABC are D, E, F, and the links