添加有用的辅助线,犹如化学反应中添加催化剂,在证几何题时常常起着关键的作用,收到“得一线而活全局”之效果。但是,添加辅助线是一项难度较大且富有灵活性和创造性的思维活动,在很多题中“添”无定法,所以学生感到难以捉摸。笔者认为,这一思维活动的全过程是按“因需思添,因题试添,因用选添”这个思 Add useful auxiliary line, as if adding catalyst in chemical reaction, the card geometry often plays a key role, received the “win-win-win situation” effect. However, adding guidelines is a difficult, flexible and creative thinking activity that adds “infinite” to many questions so students feel elusive. The author believes that the whole process of this thinking activity is based on “due to need to Tim, due to test Tim, due to the use of election Tim” this thought