**Fermat's principle $\Longrightarrow$ 5 las of light rays optics**
##### Propagation of light is rectilinear
In an homogenous and isotropice medium for its optical properties, light rays propagate in straight lines.
##### Light rays do not interact with each other
##### Law of reflection
<!--Comment for a fursther step :
Rays are geometrical constructions that indicate the direction of flow of the luminous energy
- in an homogenous medium, rays are stright lines.
- in an isotropic medium, rays
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* The **reflected ray***belongs to the incidente plane*, and is*located in the opposite side to that of the incident ray*, with regard to the normal of the surface at the impact point. **The angle of reflection $r$ is equal to the angle of incidence $i_1$ :
