在平面几何中,对于三角形,重点研究过两种特殊的三角形:一是直角三角形,二是等腰三角形。但在各种书刊中,时常见到具有另一种特殊关系的三角形——有一个内角是另一个内角的两倍的三角形,我们称这种三角形为“倍角三角形”。而对于倍角三角形没有进行过系统的研究,所以在解决有关的问题时,往往显得太麻烦。为此,本文 In plane geometry, for triangles, two special triangles have been studied: one is a right triangle and the other is an isosceles triangle. However, in various books and periodicals, it is common to see a triangle with another special relationship - a triangle with an internal angle that is twice that of another internal angle. We call this triangle a “double-angled triangle.” There is no systematic study of the double-angled triangles, so it is often too cumbersome to solve the problems involved. For this purpose, this article