1. The problem statement, all variables and given/known data https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xft1/v/t1.0-9/11161364_10206082495958864_2429387894279713850_n.jpg?oh=40982e4e4e7647918991060b6f630acc&oe=55C1808A&__gda__=1439347320_8abd4b5ce66baee04bbc345aef15ec68 In terms of the wavelength of the light λ, what is the value for the path difference x = r1 – r2 if at the point P on the screen there is: a. a dark region (and no other dark region between O and P)? b. a bright region, with one other bright region between O and P? 2. Relevant equations x = Δr = d sinƟ 3. The attempt at a solution I don't understand this at all? could someone give me a pointer to begin with please, thanks!