这里所说的“三垂”是指教科书中所说的垂直、垂线、垂足,虽然它们都有一个“垂”字,但却有着很大的区别.一、明辩概念两条直线相交所成的四个角中有一个角是直角,我们就说这两条直线相互垂直.两条直线互相垂直时,我们说其中一条直线是另外一条直线的垂线.垂足是指互相垂直的两条直线的交点,它是一个点.如图1,直线AB和CD相交于点O,且 Here we say “three vertical” refers to the textbook said vertical, vertical, vertical foot, although they all have a “vertical ”, but there is a big difference. When the two straight lines are perpendicular to each other, we say that one of the four straight lines is the perpendicular of the other straight line. Refers to the intersection of two straight lines perpendicular to each other, which is a point, as shown in Figure 1, the lines AB and CD intersect at point O, and