三角形、梯形中位线定理是平面几何中两个很重要的定理，它们都具有两个方面的特性：其一是在位置上三角形中位线平行于第三边，梯形中位线平行于上、下底；其二是在数量上三角形中位线等于第三边的一半，梯形中位线等于上、下底之和的一半．因此，它在几何计算或证明中有着广 Triangle, trapezoid median line theorem is two very important theorem in plane geometry, they all have two aspects of the characteristics: First, in the location of the triangle in the middle of the line parallel to the third side, trapezoidal median line parallel to the upper The second is that in the number of triangles, the bit line is equal to half of the third edge, and the trapezoidal median line is equal to half of the sum of the upper and lower bottoms. Therefore, it has a wide range of geometric calculations or certifications.