If the ratio of the equivalent resistance of two resistors $R_1$ and $R_2$ in series to that in parallel is $n$,then:

• A
  ${\left( {\frac{{{R_1}}}{{{R_2}}}} \right)^2} + {\left( {\frac{{{R_2}}}{{{R_1}}}} \right)^2} = {n^2}$
• B
  ${\left( {\frac{{{R_1}}}{{{R_2}}}} \right)^{3/2}} + {\left( {\frac{{{R_2}}}{{{R_1}}}} \right)^{3/2}} = {n^{3/2}}$
• C
  $\left( {\frac{{{R_1}}}{{{R_2}}}} \right) + \left( {\frac{{{R_2}}}{{{R_1}}}} \right) = n$
• D
  ${\left( {\frac{{{R_1}}}{{{R_2}}}} \right)^{1/2}} + {\left( {\frac{{{R_2}}}{{{R_1}}}} \right)^{1/2}} = {n^{1/2}}$