有些几何题常因其图形不是基本图形,因而无法直接利用基本图形的性质或有关的定理.这就需要添加适当的辅助线,使之成为我们熟知的图形(如等腰三角形、直角三角形、平行四边形、矩形、正方形、圆).然后再利用这些特殊图形的性质,来沟通题设条件与结论之间的联系.从而达到解题目的.下面举例说明. Some geometric problems often cannot directly use the nature of basic graphics or related theorems because their graphics are not basic graphics. This requires the addition of appropriate auxiliary lines to make them familiar to us (such as isosceles triangles, right triangles, parallels Quadrilaterals, rectangles, squares, circles). Then use the nature of these special graphics to communicate the connection between the conditions and the conclusions of the questions. In order to solve the problem, the following examples are given.