三角形有中位线定理,梯形有中位线定理,那么一般的四边形有无中位线定理呢? 首先,我们给四边形定义中位线:一组对边中点的连线,称四边形的中位线。而且有以下的四边形的中位线定理。命题 a,b为四边形的一组对边的长,其延长线的夹角为a(平行视为0°),则另一组对边中点的连线长为 Triangles have a median line theorem, trapezoids have a median line theorem, then the general quadrilateral with or without the median line theorem? First, we define the median line for the quadrilateral: a set of lines connecting the midpoints, called the quadrilateral Bit line. And there is the following quadrilateral median line theorem. The proposition a,b is the length of a pair of opposite sides of a quadrilateral, the angle of the extension line is a (parallel is regarded as 0°), and the length of the connection line of the middle point of the other pair is