d
\(\begin{gathered}
\Delta x\,\, = \,\,\,d\,\,sin\,\,\theta \,\, = \,\,n\,\lambda \hfill \\
0.589\,\,sin\,\theta \,\, = \,\,3\,\,\, \times \,\,589\,\,\, \times \,\,1{0^{ - 9}} \hfill \\
\theta \,\, = \,\,\,{\sin ^{ - 1}}\,\,\left[ {\frac{{3\,\, \times \,\,589\,\, \times \,\,{{10}^{ - 9}}}}{{589\,\, \times \,\,{{10}^{ - 3}}}}} \right]\,\, \hfill \\
\end{gathered} \)
\(\, \Rightarrow \,\,\theta \,\, = \,\,{\sin ^{ - 1}}\,\,[3\,\, \times \,\,{10^{ - 6}}]\)