First, a line out of plane is parallel to a line in plane, or there are intersecting lines on both sides to emphasize out of plane and in plane.

Second, the distance between two different points on the out-of-plane straight line and the surface is equal, emphasizing out-of-plane

Third, it is proved that there is no intersection between the line and the surface.

Fourth, reduction to absurdity (line and surface intersect and then overturn)

5. Space vector method, which proves a line parallel vector and an in-plane vector (x 1x2-y 1y2=0).