三角形中位线定理:三角形的中位线平行于第三边,并且等于它的一半.这是三角形的一条很重要的性质,平面几何中常用它解决直线平行和线段倍分等问题.应用这个定理证题时,常要添置必要的辅助线来创造条件,沟通已知和结论间的关系.现将几种常见的辅助线作法,介绍如下,供大家参考. Triangle’s median line theorem: The median line of a triangle is parallel to the third side and equal to half of it. This is a very important property of the triangle. It is often used in plane geometry to solve problems such as straight line parallels and line segment multiples. In the theorem testimony, it is often necessary to add the necessary auxiliary lines to create conditions and communicate the relationship between the known and the conclusions. Now several common auxiliary line practices are described below for your reference.