Here are two mirrors OD and OE the angle between them is "alpha"
The question is to find angle "beta"
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Angle-chasing usually works: (due to symmetry) (since OBA + DBC + ABC = 180 deg) (also due to symmetry) (since ACB + EC(D) + BC(D) = 180 deg)
thanks very much but why are <OBA and <DBC equal? they are not similar triangles please explain ;(
It's because the ray reflects at point B, so the angle of incidence equals the angle of reflection.
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