\({\log _{1/\sqrt 2 }}\sin x > 0\), \(x \in [0,\,4\pi ]\)\( \Rightarrow \) \(0 < \sin x < 1\)
\(\therefore\) Integral multiple of \({\pi \over 4}\) will be \({\pi \over 4},\,{{3\pi } \over 4},\,{{9\pi } \over 4},{{11\pi } \over 4}\)
Number of required values \(= 4.\)