The angle of incidence is equal to the angle of reflection.

The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.

The ratio of the sine of the angle of incidence i to the sine of the angle of refraction r is constant for the pair of given media

The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.

Any distance from perpendicular to the pole upwards is taken is positive

Any distance from the left of the pole is taken is negaitive

Any distance from perpendicular to the pole downwards is taken is negative

Any distance from the right of the pole is taken is positive