The critical angle of a certain medium is sin^-1 (3/5). The polarising angle of the medium is

we know that $\mathrm{\mu }=1/\sin \mathrm{C}$
Given that $\mathrm{C}={\sin }^{-1}(3/5)$
or $\sin \mathrm{C}=3/5\therefore \mathrm{\mu }=1/(3/5)=\frac{5}{3}$
$$\begin{gathered} \text{ If }{\mathrm{i}}_{\mathrm{p}}\text{ be the polarising angle, then } \\ \tan {\mathrm{i}}_{\mathrm{p}}=\mathrm{\mu }\text{ or }{\mathrm{i}}_{\mathrm{p}}={\tan }^{-1}\left(\mathrm{\mu }\right) \\ \text{ or }{\mathrm{i}}_{\mathrm{p}}={\tan }^{-1}(5/3) \end{gathered}$$