Thank you for reporting, we will resolve it shortly
Q.
The intensity ratio of the maxima and minima in an interference pattern produced by two coherent sources of light is 9 : 1. The intensities of the used light sources are in ratio
$\frac{I_{max}}{I_{min}}=\frac{\left(a+b\right)^{2}}{\left(a-b\right)^{2}}$
$\frac{9}{1}=\frac{\left(a+b\right)^{2}}{\left(a-b\right)^{2}}$
or $\quad \frac{3}{1}=\frac{a+b}{a-b}$ or 3a-3b = a+b
or $\quad$ 2a = 4b or a = 2b
$\therefore \quad \frac{I_{1}}{I_{2}}=\frac{a^{2}}{b^{2}}=\frac{4}{1}$