a
\(\frac{{{R_A}}}{{{R_B}}} = {\left( {\frac{{{r_B}}}{{{r_A}}}} \right)^4}\)

\( \Rightarrow \,\,\frac{{{R_A}}}{{{R_B}}} = {\left( {\frac{1}{2}} \right)^4} = \frac{1}{{16}}\)

\( \Rightarrow \,\,{R_B} = 16{R_A}\)

\(R_A\) અને \(R_B\) સમાંતર માં જોડતા

\( \Rightarrow \,\,{R_{eq}} = \frac{{{R_A}{R_B}}}{{({R_A} + {R_B})}} = \frac{{16}}{{17}}{R_A}\)

\(\therefore \,\,{R_A} = 4.25\,\Omega \,\,\) તો \({R_{eq}} = 4\,\Omega \)