1. The problem statement, all variables and given/known data It turns out there is a relation between angle a and angle b. I can't figure it out, could someone give me a hint? There's a lightray that is bouncing from two mirrors (m1 and m2). The angle between those two mirrors is called a. The angle between the incoming lightray l1 and the mirror m1 is called x. The angle between the incoming lightray l1 and the outgoing lightray l3 called b. 2. Relevant equations incoming angle it outgoing angle 3. The attempt at a solution I get stuck at the mathematical proof... Someone a clue?