A value of $\theta$ $\in$ (0, $\pi$/3), for which  \left| {\begin{array}{*{20}{c}} {1 + {{\cos }^2}\theta }{{{\sin }^2}\theta }{4\cos 6\theta } \\ {{{\cos }^2}\theta }{1 + {{\sin }^2}\theta }{4\cos 6\theta } \\ {{{\cos }^2}\theta }{{{\sin }^2}\theta }{1 + 4\cos 6\theta } \end{array}} \right| = \,0, is