学生都知道切线的判定定理,但是几乎少有学生去深刻剖析切线的判定定理,因此也就很难发现切线判定定理中的奥妙所在。切线的判定定理是:经过半径的外端并且垂直于这条半径的直线是圆的切线。仔细观察,就会发现这段话中的“半径的外端点”有着丰富的含义,首先该点是在圆上,其次经过该点的直线垂直于过这个点的半径。因此, Students all know the theorem of tangential decision, but few students deeply analyze the decision theorem of tangential line, so it is hard to find out the mystery of tangential decision theorem. The tangential decision theorem is that the straight line passing the outer end of the radius and perpendicular to this radius is a tangent to the circle. After careful observation, you will find that the “outer end of radius” in this passage has a rich meaning. First, the point is on the circle, and secondly, the straight line passing through the point is perpendicular to the radius of the point. therefore,