圆是几何中最简单、同时又是最重要的一种曲线,与圆有关的概念经常遇到的有:同心圆,多边形的外接圆,多边形的内切圆,三角形的旁切圆,点圆,单位圆等。下面再介绍几种圆。 费尔巴哈圆:三角形三边的中点,三高的垂足,连结垂心与顶点的三线段的中点,这九个点共圆,这个圆叫九点圆,又叫费尔巴哈圆。 托里拆利圆:在△ABC的三边AB、BC、CA上各向外侧作等边三角形。这三个等边三角形 The circle is the simplest and at the same time the most important kind of curve in the geometry. The concepts related to circles are often encountered: concentric circles, circumscribed circles of polygons, inscribed circles of polygons, side cut circles of triangles, point circles , Unit circle and so on. The following describes several types of circles. Feuerbach’s circle: The midpoints of the three sides of the triangle, the three-pronged foot, the midpoint of the three-line segment linking the vertical and the apex. These nine points are all round. This circle is called nine-point circle, also known as Feuerbach. round. Torelli Circle: An equilateral triangle on the three sides AB, BC, and CA of ABC. The three equilateral triangles