(本讲适合初中) 在同一平面内,不相交的两条直线叫平行线。平行线是初中平面几何最基本的,也是非常重要的图形。在证明某些平面几何问题时,若能依据证题的需要,添加恰当的平行线,则能使证明顺畅、简洁。 添加平行线证题,一般有如下四种情况。 (This lecture is suitable for junior high school.) In the same plane, two lines that do not intersect are called parallel lines. Parallel lines are the most basic and very important graphics for junior high school plane geometry. When proving certain plane geometry problems, if we can add appropriate parallel lines according to the needs of the questions, we can make the proof smooth and concise. Adding parallel line test questions generally has the following four conditions.