How to find the plane angle of dihedral angle?

How to find the plane angle of dihedral angle?


1. Through the same point respectively, make the vertical lines of the intersection lines of two planes in two planes. The angle between the two intersection lines is the plane angle corresponding to the dihedral angle
2. If you can make a vertical plane through a point on the edge, the angle formed by the intersection of two planes is the plane angle



The plane of the dihedral angle is perpendicular to both sides of the dihedral angle
I don't quite understand this sentence,


The first is the dihedral angle, which is the angle formed by the intersection of two planes
The plane angle is a point on the edge where two planes intersect, making a straight line in two planes perpendicular to the edge where two planes intersect
The two lines are in the same plane, which is perpendicular to the previous two planes



If the two ends of a line segment are respectively in the two planes of a straight dihedral angle (not on the edge), then the sum of the angles formed by the line segment and the two planes is - 90 degrees


If the two ends of a line segment are respectively in the two planes of a straight dihedral angle (not on the edge), then the sum of the angles formed by the line segment and the two planes