How do I find the limiting expression formula for delta k using part (a)? For part (a) I got
$$F(k) = \frac1{ i(k_o -k) } \left( e^{ \frac{i a }2 (k_o - k) } - e^{ \frac{-ia}2 (k_o - k) } \right) \\ |F(k)|^2 = \frac1{(-k + ik_o)^2} \left( 2+2e^{ia(k_o -k)}\right) $$
Any help will be very appreciated. Thanks!