4. IE •• Two upright plane mirrors touch along one edge, where their planes make an angle of α. A beam of light is directed onto one of the mirrors at an angle of incidence of β (β < α) and is reflected onto the other mirror.

(a) Will the angle of reflection of the beam from the second mirror be (1) α, (2) β, (3) α + β, or (4) α − β?

(b) If α = 60° and β = 40°, what will be the angle of reflection of the beam from the second mirror?