I am to prove that in y = R * m * (wavelength) / a where y is the distance between two minima, a is the width of the slit, R is the length between the screen and the slit grating, and m is an integer which is the order of the minima. I know I have to use the paraxial approximation where tan x is approximately sin x which is approx. x, but I can't seem to apply it. When I refer to my textbooks, they state that y is the difference between the central maximum and the first minimum when m=1. Is this applicable bet. two minima as well?