Width of principle maxima in n slit diffraction

[Sharlom]

I was working on derivation to find the witdh of principle maxima in n slit diffraction
Angular width=2Δθ_m=2λ/(Ndcosθ_m)
Where d:distance between slits
θ_m:angle at which m^th order principle maxima is present.
N:no. Of slits

#in the diagram given below why the minima just adjacent to mth pricinple maxima is written as mN±1
*the thing I know is that this mN±1 is related to the fact that there are N-1 minimas present b/w 2 consecutive principle maximas
How that I 'm not able to relate it?

 

[BvU]

Hi there,

Please don't delete the template but use it. If not for you, then for those of us who want to help.

Hyperphysics has an expression for the intensity. You can derive the widths from that.

 

[Sharlom]

My actual doubt is how that mN±1 came ?