Makes one after system's non-balance point M in each spot the tangential path which does not contact with this system's gago line, namely in each spot with direction different tangential path. We said that this kind of line segment to not cut the line segment, records makes L., because selects M right and wrong balance point M, also P (x, y) with Q(x, y) continuously, therefore this kind not cuts the line segment to do comes out Makes one after system's non-balance point M in each spot the tangential path which does not contact with this system's gago line, namely in each spot with direction different tangential path. We said that this kind of line segment to not cut the line segment, records makes L., because selects M right and wrong balance point M, also P (x, y) with Q(x, y) continuously, therefore this kind not cuts the line segment to do comes out