解答初中几何题时,有关辅助线的添加往往都归结到一些基本图形的构造和基本结论的应用。下面笔者以一道中考题为例,通过构造基本图形,使其解法自然生成。1题目如图1,半圆O的直径AB=10 cm,弦AC=6 cm,AD平分∠BAC,则AD的长为()。 When answering the question of geometry in junior high school, the addition of the auxiliary line always comes down to the application of some basic graphic constructions and basic conclusions. The following author to a test questions, for example, through the construction of basic graphics, so that its natural solution. 1 title shown in Figure 1, the semicircle O diameter AB = 10 cm, chord AC = 6 cm, AD bisects ∠ BAC, AD length ().