According to the three principles of "two angles are equal", "three lines are flat" and "two lines are separated", the reflection of incident light in space is indeed
There is only one light, so the position of the reflected light is accurately determined. Both cardboard 1 and 2 conform to the three principles, but cardboard 1 obviously does not conform to life experience.
The significance of introducing normal is to let people know that the plane where incident light and reflected light are located is perpendicular to the mirror.
Therefore, the cardboard 2 is legal.