How to find dihedral angle

The techniques for finding dihedral angles are as follows:

1, vertical plane method-the angle formed by the intersection of a straight line perpendicular to the edge with the vertical plane and dihedral angle, namely dihedral angle and planar angle.

2. Definition method-take any point on the edge so that the perpendicular of point A on the edge lies in two planes. Sometimes we can make this vertical line into two different planes, and then find the dihedral angle on a parallel line with the vertical line.