What are the solutions of dihedral angle in high school solid geometry? I wish I could be more specific.

(1) definition method (basic): perpendicular to the intersecting straight lines respectively, find the included angle between the two straight lines;

(2) the vertical plane method (rarely used): find the vertical plane of the intersection line, make the intersection line between the vertical plane and the half plane, and find the included angle;

(3) Three perpendicularity method (commonly used): a point on one half plane is perpendicular to the other half plane and the intersection line, and the projection is solved by tan angle;

(4) Vector method (universal): Make the normal vectors of two half-planes, respectively, and get them from the vector included angle formula. Note that the included angle is not a dihedral angle, but its complementary angle!

(5) Projection area method (commonly used): the cosine of dihedral angle is equal to the ratio of the projected area of one half plane on another half plane to the area of the plane itself.

This is the basic idea, and there are many skills in it, such as finding the length of the vertical line and the normal vector by the equal volume method, so I won't say much here.