Don't talk nonsense if you don't understand. Yes, I don't want to say the first question. Dihedral angle α-DE-C can be divided into α-DE-B and B angle α-de-c. . . I see. The dihedral angle can be obtained by the area method. It is easy to prove that the projection of point C on the plane BDE is point B, and cos(B-DE-C) is equal to the area of BDE divided by the area DEC. Similarly, point F in BD is the projection of point A on the surface BDE. As for how to calculate the area, cosine theorem and sine theorem can be used. I like to solve problems by traditional methods in college entrance examination, because it is convenient to use and the coordinate method is too limited. If you are not familiar with this problem, you can use the coordinate method because there is a ready-made coordinate system. . .