Correlation calculation method of dihedral angle

I think the more practical method, the teacher just helped us summarize:

1 Definition method: directly calculate the plane angle of dihedral angle. Take a point (special point) on the intersection of two dihedral angles as the perpendicular to the edges in two half planes, and the included angle is the plane angle of dihedral angles.

2 Three-perpendicular method: given the plane angle, the perpendicular from point A in one plane to another plane, the vertical foot B is the perpendicular of the side, intersects with the side C, connects AC, and the angle ACB is the plane angle of dihedral angle.

As for other methods, I won't introduce them. If you master the above two methods, I guarantee that 99% of the questions can be worked out.

There is also a dihedral angle problem without edges.

1 Draw a hidden edge, usually find a line parallel to the two halves of the plane.

2 extend the surface and find the edge.