Two waves of intensity ratio 1:9 cross each other at a point. The resultant intensities at that point, when (a) Waves are incoherent is I_1 (b) Waves…

Two waves of intensity ratio $\displaystyle 1$:$\displaystyle 9$ cross each other at a point. The resultant intensities at that point, when (a) Waves are incoherent is $\displaystyle I_1$ (b) Waves are coherent is $\displaystyle I_2$ and differ in phase by $\displaystyle 60^{\circ}$. If $\displaystyle \frac{I_1}{I_2}=\frac{10}{x}$ then $\displaystyle x=$ $\displaystyle \_\_\_\_$.