The angle of incidence is equal to the angle of reflection. This is the core idea behind the law of reflection.
Both angles are measured from the normal line, which is an imaginary line drawn perpendicular to the surface at the point where the light ray hits it.
So, if a light ray strikes a surface at an angle of 40 degrees to the normal, it will reflect off the surface at the same 40-degree angle on the other side of the normal. This relationship holds true for all smooth, reflective surfaces like mirrors.
This equal-angle relationship helps predict the direction of reflected light and is used in designing optical instruments like periscopes, mirrors, and laser systems.