1 system. Taking the intersection of three vertical lines as the origin, auxiliary lines are needed when there are no three vertical lines; Establish a right-handed rectangular coordinate system so that as many points as possible fall on the coordinate axis.

2 Set a point. Sometimes it is necessary to set the length of a line segment to a, and write all the relevant points, usually four, with two points on the intersection of two sides, M and N, plus one point on each side, A and B.

3 Find the direction vector. Use arrows to find the direction vectors AM, AN and BM, BN on both sides respectively.

4 Find the normal vectors m and n, and let m=(x 1, y 1, z 1) and n=(x2, y2, z2) respectively; Using the normal vector perpendicular to the direction vector, whose product is 0, two ternary linear equations can be listed; Let x 1= an exact number, such as 1 or 0, and find the other two coordinates. Similarly, you can find the n vector (note that the normal vector needs to be a non-zero vector).

5 Find the included angle β of two normal vectors, and observe the orientation of normal vectors M and N in the spatial rectangular coordinate system, whether it is in-plane or out-of-plane.