我们知道,“在同一个平面内,不相交的两条直线叫做平行线.”因此,如果不交待不相交的两条直线在同一个平面内,我们说这两条直线一定平行,那么就错了!请看实例: 图1是长方体的模型.因为两棱AB与A′B′在同一个平面ABB′A′内,又无论怎样把棱AB与A′B′分别向两方延长,它们总不会相交,因此能下结论:AB//A′B′.同样,棱AB与D′C′ We know, “In the same plane, the two lines that do not intersect are called parallel lines.” Therefore, if we do not talk about the two lines that are not intersecting in the same plane, we say that the two lines must be parallel, then we’re wrong. Let’s look at the example: Figure 1 shows the model of a rectangular parallelepiped. Because the two edges AB and A′B′ are in the same plane ABB′A′, and no matter how the edges AB and A′B′ are extended to two sides respectively, they It does not intersect, so it can be concluded: AB/A′B′. Similarly, edges AB and D′C′