The angle of reflection is the angle the to the reflecting surface.
reflected rays make with a perpendicular line
instant raise makes with a perpendicular line
instant ray makes with a parallel line
reflected ray mix with a parallel line

The angle of reflection is the angle the reflected rays make with a perpendicular line to the reflecting surface.  

Explanation:

Reflection It is the change of direction suffered by a luminous ray when hitting the surface of an object. The angle of reflection is that which is formed by the reflected ray and the normal vector to the study surface

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