我们知道,连接三角形一边中点和对角顶点的线段叫做三角形的中线.三角形的中线是三角形的重要的“三线”(中线、角平分线、高线)之一.三角形的中线与周长、面积的结合,以及利用三角形的中线构造全等三角形,都是最常见的出题形式.例1(1)图1为一块三角形土地ABC,其面积为120m~2.已知BD是AC边上的中线,那么S_△BDC=A m~2;又知点E是线段DC We know that the line connecting the middle and diagonal vertices of a triangle is called the center line of the triangle The center line of the triangle is one of the important “three lines” (center line, angle bisector, high line) of the triangle. The combination of length and area, as well as the construction of congruent triangles using the center line of the triangle, are the most common forms of the problem. Example 1 (1) Figure 1 shows a triangle of land ABC with an area of ​​120 m 2. On the edge of the center line, then S_ △ BDC = A m ~ 2; and point E is the line segment DC