(1): [1] The midline of the triangle is parallel to the third side, which is equal to half of it. As shown in the figure, the connecting line (median line) between the midpoints of two sides of the triangle is parallel to the BC side and equal to half of the third side. The area of the small triangle (midpoint triangle) formed by the center line of the triangle is one quarter of the area of the original triangle. The triangle formed by the three center lines of the triangle is a figure similar to the original triangle.