Every geometric theorem has its corresponding geometric figure, which we call basic figure. Adding auxiliary lines often has the nature of basic graphics, which can be supplemented when the basic graphics are incomplete, so "adding lines" should be called "supplementing graphics"! This can prevent adding lines indiscriminately, and adding auxiliary lines has rules to follow. The basic figure of the hypotenuse midline of a right triangle

The midpoint on the hypotenuse of a right triangle is often added to the midline on the hypotenuse. If the line segment is the hypotenuse of a right triangle, it is necessary to add the midline on the hypotenuse of the right triangle to get the basic figure of the midline on the hypotenuse of the right triangle.