With F as the origin, FA as the positive direction of X axis, FE as the positive direction of Y axis, and the vertical line passing through F as the Z axis. Plane ABEF is xFy plane, z = 0；;
The EFDC plane is on the yFz plane. According to symmetry, E-BC-A and F-AD-B are equal.
Write the equations of plane AFD and ABD, and find the normal vectors of the two planes. The cosine of the angle between two planes can be found by the dot product of two normal vectors.
The story of the middle class 1
Activity objectives:
1. Understand the story and learn the main dialogue