Two coherent plane light waves propagating with a divergence angle < < I fall almost normally on a screen. The amplitudes of the waves are

Two coherent plane light waves propagating with a divergence angle ψ << I fall almost normally on a screen. The amplitudes of the waves are equal. Demonstrate that the distance between the neighbouring maxima on the screen is equal to ∆x = λ/ψ, where λ, is the wavelength.