史坦纳(Steiner)定理:如果三角形的两条角平分线相等,则此三角形为等腰三角形。这个定理貌似简单,其实是采用直接法证明的有名的世界难题,经不少学者的关注,至今已有60多种证法。下面看Hesse给出的证明。 Steiner Theorem: If the bisectors of the two angles of a triangle are equal, the triangle is an isosceles triangle. This theorem seems to be simple. In fact, it is a famous world problem that has been proved by the direct method. After many scholars have paid attention to it, there are more than 60 kinds of evidence. See the proof given by Hesse below.