The Kaplan Physical Science Review Notes (p. 348 and 349 for anyone who currently has them) confused me. First they talk about diffraction when light passes through a small slit and say: The location of the dark fringes (minima) is given by the following formula: (a)sin(theta) = n(lambda) Then, on the next page when talking about interference and Young's double slit experiment they list the maxima as (d)sin(theta) = m(lambda) and minima as (d)sin(theta) = (m+1/2)(lambda). In these two formulas, d and a are the same thing (the width of the slit). So which is it? It seems the two discussions are contradicting each other, so did Kaplan mess up or am I missing something here?