# While I was reading an article about diffraction of light on

On the formalism of the angular position of the first minima, it assumes that the light from a source located at the top edge of the slit interferes destructively with a source located at the middle of the slit, when the path difference between them is equal to λ/2. Similarly, the source just below the top of the slit will interfere destructively with the source located just below the middle of the slit at the same angle. Therefore, (d/2)sinθ=λ/2, dsinθ=λ (1), where θ is the angular position of the first minima.

I wonder if I changed the assumption to assumes that the light from a source located at the top edge of the slit interferes CONSTRUCTIVELY with a source located at the middle of the slit, when the path difference between them is equal to λ/.I will get dsinβ=2λ (2), where β is the angular position of the first maxima. I know that equation (2) is wrong, the correct equation should be dsinβ=3λ/2. My question is why we can't formulate the equation as straight forward as we did in formulating the equation for the interference pattern formed in Young's experiment.