‌‌ For ‌n‌th ‌‌ minima ‌ ‌bsin‌θ=nλ ‌(λ‌ is ‌smallsosin‌θ‌ is small, hence ‌sin‌θ≃tan‌θ) ‌b‌tan‌θ=nλ ‌b‌
y
D
=nλ ‌⇒yn=‌
nλD
b
‌ (Position of ‌n‌th ‌‌ minima) ‌
‌B⟶1st‌ minima, ‌A⟶3‌rd ‌‌ minima ‌ ‌y3=‌