erm anyone knows why for destructive interference to occur for a fraunhofer's diffraction pattern, the equation is a/2sin(theta) = m(lamda)/2 , ==> sin(theta) = m(lamda)/a ? where a = slit width lamda = wavelength theta = angle the ray makes with the central axis the problem i have here is with the value "m" takes. the textbook i am using says that "m" ranges from 1,2,3,4, etc but no 0 . but if m takes on the value 2,4,6 etc, wouldn't the path difference of a/2sin(theta) be equals to 1,2,3 etc lamda ? which is a complete wavelength, hence the light would meet in phase and be constructive? so why is "m" be able to take on the values 1,2,3,4,5 etc... i know it doesn't take on 0 because the central fringe is always bright.