等腰三角形是一种特殊的三角形．也是常见的基本图形．它除了具有三角形的一切性质外，还有其特殊性质：1．两底角相等；2．项角平分线、底边上的中线、底边上的高互相重合．在解几何题时，灵活应用等腰三角形的这些性质，可巧妙、迅捷地证明若干与角、线段有关的几何题．例1如 Isosceles triangle is a special kind of triangle. Is also a common basic graphics. In addition to having all the properties of a triangle, it has its special properties: 1. The two bottom corners are equal; The bisector of the angle, the midline on the bottom, and the height on the bottom coincide with each other. When solving geometric problems, flexible use of these properties of isosceles triangles can be used to subtly and quickly prove some geometric problems related to angles and line segments. Example 1