Property Theorem of Octagonal Triangle

The property theorem of a splayed triangle is that the sum of two sides of the triangle is greater than the third side. The difference between the two sides is smaller than the third side. The unfolding triangle is located on both sides of the cutting line and inside the cutting line. The cross section of the inner corner is "Z" or "N". Two straight lines are cut into eight angles by a straight line. The first and second straight lines are called cutting lines, and the third straight line is called cutting line.