这是古稀老人张光禄先生在数学中的一个小小发现,“定理”本身看似平凡,但用之往往见奇效.张先生一辈子都坚守供电工作岗位,但在业余用这个“分角定理”巧妙地证明了“三弦定理”、“张角定理”和“三割线定理”等,特别地,简单解决了梁绍鸿先生收入《初等数学复习及研究(平面几何)》一书的一个矩形半圆问题,这道题国内给出的解法,大多“太繁,不忍卒谈”. This is a small discovery by Mr. Zhang Guanglu, an old man of ancient rare age, in mathematics. The theorem itself seems to be ordinary, but it is often used to see the effect. Mr. Zhang has been sticking to the power supply job all his life, but he uses this “angle” in his spare time. Theorem “Splendidly proved ”the Sanxian Theorem “, ”Angle Angle Theorem“ and ”Triangle Theorem“, etc. In particular, it simply solved Mr. Liang Shaohong’s income ”Elementary Mathematics Review and Research (Flat geometry ) A rectangular semi-circle problem of the book. The solution given in this question is mostly “too complicated and not worthy of discussion”.