Why can this formula be applied for diffraction gratings?

[Dragynfyre]

So for 2 point sources (or 2 slits) the formula for finding the lines of maxima and minima for waves is n(lambda)=dsin(theta) and when n is an integer you would expect to find a maxima. However, I don't understand why this formula also applies to diffraction gratings since there are way more than 2 slits. So can anyone explain this to me?

 

[ehild]

Consider the grating as pairs of slits. All pairs produce maxima or minima.

ehild