How to prove dihedral angle and how to find two and a half planes of dihedral angle in high school mathematics problems, it is best to have examples.
A straight line in a plane divides a plane into two "half planes", and the two "half planes" starting from a straight line form a figure, which is a dihedral angle. This straight line is called the edge of dihedral angle, and these two "half planes" are called the faces of dihedral angle. The intersection of the plane perpendicular to the edge and the dihedral angle forms the plane angle of the dihedral angle. The plane angle is a dihedral angle.