Angular midline property: the midline of a triangle is parallel to the third side and equal to half of it. A triangle composed of three midlines of a triangle is similar to the original triangle.
The midline of a triangle should be distinguished from the midline of a triangle. The midline of a triangle is the midpoint connecting the vertex and its opposite side, while the midline of a triangle is the line segment connecting the midpoints of both sides of the triangle.
Inverse theorem of triangle midline theorem
Inverse theorem 1: As shown in figure DE//BC, DE=BC/2, then D is the midpoint of AB and E is the midpoint of AC. Inverse Theorem 2: If Figure D is the midpoint of AB and de//BC, then E is the midpoint of AC, and DE=BC/2 proves that ① Take the midpoint of AC and connect DG, then DG is the centerline of triangle ABC ∴DG∥BC and ∨ DE ∨ BC ∴ DG coincides with DE (slightly beyond the straight line, only one.