1. The problem statement, all variables and given/known data Find at which angles θ the interference picture that appears on a distant screen made by three thin slits separated by distance d and enlightened by a source of wavelength λ (see figure) a) Shows its maxima. b) Shows its minima. multiple slit diffraction, d, ##\lambda##, ##\theta## 2. Relevant equations $$dsin\theta=m\lambda$$ $$dsin\theta=(m\lambda)/3$$ $$E(t)=E_0cos(k(r_2-r_1)-\omega(t))$$ $$t=top,m=middle,b=bottom$$ 3. The attempt at a solution $$E_t=E_0cos(k(r_t-r_b)-\omega(t))$$ $$E_m=E_0cos(k(r_t-r_m)-\omega(t))$$ $$E_b=E_0cos(-\omega(t))$$ However, the solutions gives me something like this. My thought process was that the top ray travels the most or has the biggest path difference. I don't get why the solutions give me these equations. Or am I getting my path differences mixed up? Thanks for the help.