一、三角形中位线的定义连接三角形两边中点的线段叫做三角形的中位线.三角形有三条边,所以三角形的中位线有三条,如图1所示:如果点D、E、F分别是AB、BC、CA的中点,那么线段DE、EF、FD都是三角形的中位线.例1如图2所示,在△ABC中,AB=8cm,AC=10cm,D、E分别是AB、AC的中点,并且AD=4cm,CE=5cm,则下列线段中是 First, the definition of the median line in the triangle The middle line connecting the two sides of the triangle is called the median line of the triangle.There are three sides of the triangle, so the triangular median line has three, as shown in Figure 1: If the points D, E, F, respectively Is the midpoint of AB, BC, CA, then the segments DE, EF and FD are both triangular median lines Example 1 As shown in Fig. 2, in ABC, AB = 8cm, AC = 10cm, D, E Is the midpoint of AB, AC, and AD = 4 cm, CE = 5 cm, then yes in the following line