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在直线与圆的位置关系中 ,相切关系很重要 .要掌握“切线证明”的思路和方法 ,首先要搞清切线的判定方法有哪些 ?切线的判定方法有 :①直线l与⊙O有且只有一个交点时 ,直线l与⊙O相切 .②圆心O到l的距离d =r ,则直线l与⊙O相切 .③经过半径外端并且垂直于半径的直线是圆的切线
In the positional relationship between the straight line and the circle, the tangent relationship is very important. To grasp the idea and method of “tangential proof”, first of all, what are the methods for determining the tangent? The tangent determination methods are as follows: 1 Line l and ⊙O And when there is only one intersection point, the straight line l is tangent to ⊙O. 2 The distance from the center O to l is d = r, then the straight line l is tangent to ⊙O. 3 The straight line passing through the outer end of the radius and perpendicular to the radius is the tangent of the circle.