Diffraction of light at a single slit, the pattern obtained consists of a central bright band having alternate dark and weak bands of decreasing intensity on both sides. For nth minima (secondary), sin‌θn=
nλ
a
For nth maxima (secondary), sin‌θn=(2n+1)
λ
2a
Thus, point 5 corresponds to path difference of extreme rays equal to 2λ.