“若△ABC是等腰三角形,则两底角B、C的平分线BD、CE的长度相等”,这个命题的证明是很容易的,但它的逆命题“着△ABC的角B、角C的平分线BD、CE的长度相等,则△ABC是等腰三角形”用直接证明方法来证明却是很不容易的。我想,许多读者都知道,这是一个有名的难题。最近,我发现了一个直接证明它的方法,在此作一介绍: “If △ABC is an isosceles triangle, then the bisecting lines BD and CE of the two base angles B and C are equal in length”, this proof of proposition is very easy, but its opposite proposition "angle B, angle of ABC The lengths of the bisectors BD and CE of C are equal, then △ABC is an isosceles triangle. It is not easy to prove it by the direct proof method. I think many readers know that this is a well-known problem. Recently, I found a way to directly prove it. Here’s an introduction: