# Double-slit problem with incident and refracted angles

1. Homework Statement
For the given configuration, the path difference between the 2 rays is given as δ=dsinθ1 - dsinθ2

2. Homework Equations
Small angle approximation?

3. The Attempt at a Solution
I'm used to seeing a double-slit situation where only the exit angle is specified, and thus path difference is simply δ=dsinθ. Here, though, we have an incident and refracted θ1 and θ2. Any hints at deriving the following will be appreciated:

δ=dsinθ1 - dsinθ2