证明直线是圆的切线的问题,大都需要添作适当的辅助线。对此,同学们往往感到棘手。其实,只要掌握了下面两大“绝招”,这类问题就容易解决了。 绝招一:连半径,证垂直。 若图形中已给出直线与圆的公共点,但未给出过公共点的半径,则可先连出过公共点的半径。再证其与直线垂直。即“连半径,证垂直”。 To prove that a straight line is a tangent to a circle, most of them need to be added as appropriate auxiliary lines. In this regard, students often feel troubled. In fact, as long as we have mastered the following two “trick”, such problems can be easily solved. A trick: even the radius, card vertical. If the graph has given the common point of the straight line and the circle, but has not given the radius of the common point, the radius of the common point can be connected first. Again, it is perpendicular to the straight line. That is “even the radius, card vertical.”