圆是轴对称图形,任何过圆心的直线都是对称轴;圆还是中心对称图形,且圆绕圆心旋转任意一个角度β,都能与原来的图形重合。即圆有对称性利旋转不变性,因此中考试题中出现了大量训练周密思维能力的双解佳题,现分类赏析之。一、已知圆的半径和两条子弦,求两平 The circle is an axisymmetric figure. Any line that passes through a circle is an axis of symmetry; a circle is also a center symmetrical figure, and the circle rotates around the center of the circle at any angle β, which can coincide with the original figure. That is, the circle has symmetry and interest rotation invariance, so there are a large number of dual-solutions and good questions in the mid-test questions, which are closely related to the careful thinking ability. First, the radius of the known circle and two substrings, seeking two levels