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近几年的各地中考试题中,出现了一类多边形容圆问题。它不是一般的三角形的内切圆问题,而是在四边形内容有一个圆(或圆的部分),或者容有两个圆(或圆的部分),圆与四边形的某边相切。 这类问题的本质特征,是直线形(边)与圆(或圆弧)相切,所以主要是考查与切线有关的基础知识,如弦切角、圆心角、圆周角知识;切线长定理、切割线定理,等等。
In recent years, a series of polygon tolerance problems have appeared in the middle school examination questions. It is not a general triangle inscribed circle problem, but in the quadrilateral content has a circle (or circle part), or contains two circles (or a circle part), the circle is tangent to a certain side of the quadrilateral. The essential feature of this kind of problem is that the straight line (edge) is tangent to the circle (or arc), so the basic knowledge related to the tangent line is mainly examined, such as chord angle, center angle, and circumferential angle knowledge; the tangent length theorem, Cutting line theorem, and so on.