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和圆的切线相关的试题,近几年中考出现较多.在判定直线与圆相切时,要仔细观察试题中的条件特征,灵活选择方法.证题方法是“有点连半径,无点做垂直”.一、已知直线与圆有公共点时,常用切线的判定定理经过半径的外端并且垂直于这条半径的直线是圆的切线,基本思路是连接公共点和圆心,只要设法证明这个半径垂直于直线即可,简称为“连半径,证垂直”.
And the tangent of the circle related questions, in recent years more than the middle school entrance examination in determining the line tangent to the circle, we should carefully observe the conditions in the test questions, flexible choice of method. The question method is “a little radius, no point Vertical line. ”1. It is known that when a straight line and a circle have a common point, the theorem of common tangent is that the straight line passing through the outer radius and perpendicular to this radius is a tangent to the circle. The basic idea is to connect the common points and the center of the circle, Try to prove that this radius perpendicular to the line can be referred to as “with radius, vertical ”.