在初中平面几何中,经常会遇到三角形中一个内角是另一个内角二倍的问题(本文简称“二倍角”问题),这类问题往往需要作相应的辅助线.因为等腰三角形顶角的外角是其任一底角的二倍,因而构建等腰三角形是 In the junior middle school geometry, often encounter one of the triangles is one corner of the other two times the angle (this article referred to as “double angle ”), these problems often need to make the corresponding auxiliary line.Because the isosceles triangle top The outer corner of the corner is twice as long as any of its base angles, so constructing an isosceles triangle is