考点1圆的基本性质[知识要点]1.圆是平面上到的距离等于的点的集合.2.的三点确定一个圆;任何一个三角形都有一个外接圆,外接圆的圆心叫做三角形的心,它是三角形的的交点.3.圆是以为对称轴的轴对称图形,又是以为中心的中心对称图形.4.垂径定理的条件是,结论是.5.在同圆或等圆中, The basic nature of test point 1 circle [Knowledge points] 1. The circle is the set of points on the plane equal to the distance. The three points of the 2 determine a circle; any one triangle has a circumscribed circle, the center of the circumscribed circle is called a triangle The heart, which is the intersection of the triangles. 3. The circle is an axisymmetric figure of the axis of symmetry, and it is also the center of the symmetrical figure. 4. The condition of the vertical trail theorem is that the conclusion is .5. in the same circle or equal circle in,