a
For dispersion without deviation, the necessary condition is

\(\frac{A_{2}}{A_{1}}=-\frac{\mu_{1}-1}{\mu_{2}-1}=-\frac{(1.54-1)}{(1.72-1)}=-\frac{0.54}{0.72}\)

or, \(\quad \mathrm{A}_{2}=\frac{0.54}{0.72} \times 6^{\circ}=4.5^{\circ} \approx 4^{\circ} 30^{\prime}\)