The equation R = 0.61λ/sin(θ) is derived from the principles of diffraction, specifically related to electron scattering off a nucleus. It relates the radius of the nucleus to the wavelength of the electrons and the angle of diffraction. The discussion references Babinet's principle and the diffraction pattern produced by a circular disk, where the angle θ corresponds to the first minimum in the diffraction pattern. The relationship D = 2R connects the diameter of the nucleus to its radius. Overall, the equation provides a method for estimating nuclear radius using electron diffraction data.