1 is based on Problem 24.55

2 is based on Problem 27.2

3 is based on Problem 27.7

4 is based on the double-slit interference derivation (Figure 27.3),
with the added tweak of an index-of-defraction altered wavelength
(Equation 25.3 or 27.9).

5 is based on Problem 27.15

6 combines the phase difference from Equation 27.7 with vector
addition for the Electric field amplitudes.