Thread: Angles Problem

Here are two mirrors OD and OE the angle between them is "alpha"

The question is to find angle "beta"

Help Please!

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.