平面几何证题中经常需要添恰当的辅助线,而辅助线的作法又千变万化,形成几何法证题中的一个难点。本文应用正,余弦定理可巧妙地将演绎推理的论证转化为数与式的运算,且不需添加辅助线。现举例介绍如下: 一证线段相等问题例1.延长⊙O的两弦AB、CD交于圆外一点E,过E作 It is often necessary to add proper auxiliary lines in the plane geometry test, and the auxiliary line’s practice is ever-changing, forming a difficult point in the geometric method. In this paper, the positive cosine theorem can be used to subtly transform deductive reasoning arguments into mathematical calculations without adding auxiliary lines. The following is an example to introduce as follows: 1. Equivalent problem of a line segment 1. Extend the two chords of ⊙O. AB and CD cross at a point outside the circle. E