The verticality of line and plane proves the verticality of plane (A is perpendicular to plane ABC, A belongs to plane DEF, and plane ABC is perpendicular to plane DEF).

Method 2

One side is known to be vertical.

The other side is parallel to one side.

Method 3

Syndrome dihedral angle

90 (nonsense)

Method 4

The normal vector is vertical (it is too much trouble for you to find a special dihedral angle, so it is not recommended).

High school method one

Is omnipotent.

You don't have to master too much.

invalid

There is still no big problem.