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 are coherent is \( I_2 \) and differ in phase by \( 60^\circ \). If \( \dfrac{I_1}{I_2} = \dfrac{10}{x} \) then \( x = \_\_\_\_\_\_\_\_ \).
