在许多考试及相关的测试题中,涉及圆中成比例线段的问题比较常见,解决此类问题常有下面介绍的三种基本方法,请看题例分析.一、平行割线定理的运用例1如图1,在⊙O中,AB为圆的直径,BD为圆的弦,E为AB上一点,作EF⊥DB,垂足为F,若AE︰EB=1︰5,且DF=2,则BD=. In many exams and related test questions, the problem involving proportional segments of the circle is common, and the following three basic methods are often used to solve such problems. See the example analysis. First, the application of the parallel secant theorem 1, in ⊙O, AB is the diameter of a circle, BD is a round chord, E is the last point of AB, is EF ⊥ DB, and the foot is F, if AE: EB = 1︰5 and DF = 2, then BD =.