Explanation

(a) $\frac{1}{\lambda_{\min}} = R\left\lbrack \frac{1}{2^{2}} - \frac{1}{3^{2}} \right\rbrack = \frac{R \times 5}{36}$
$\frac{1}{\lambda_{\max}} = R\left\lbrack \frac{1}{2^{2}} - \frac{1}{\infty} \right\rbrack = \frac{R}{4}$
$\frac{\lambda_{\min}}{\lambda_{\max}} = \frac{R \times 5}{36} \times \frac{4}{R} = \frac{5}{9}$