The difference is that the geometric model is a template and the geometric auxiliary line is a line. The congruence angle and internal dislocation angle of the geometric model are equal, and they are interrelated.

Obviously, the model is incomplete and the conditions cannot be linked and applied. Making auxiliary lines is equivalent to completing the mathematical model. So under what circumstances can we skillfully and efficiently make auxiliary lines? Or have similar experience in solving similar problems before; Or we can judge the model contained in the question according to its meaning, and then add auxiliary lines to complete the incomplete part.