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切线的判定方法有三种:(1)和圆只有一个公共点的直线是圆的切线;(2)和圆心的距离等于半径的直线是圆的切线;(3)过半径的外端且和半径垂直的直线是圆的切线。
There are three ways to determine the tangent: (1) The straight line with only one common point in the circle is the tangent of the circle; (2) The straight line with the center of the circle equal to the radius is the tangent of the circle; (3) The outer end of the over radius and the radius The vertical line is a circle tangent.