$3\operatorname{Sin}(\frac{\pi }{4}-2x)=0\Rightarrow -3\operatorname{Sin}(2x-\frac{\pi }{4})=0$  $2x-\frac{\pi }{4}=k\pi \Rightarrow 2x=k\pi +\frac{\pi }{4}\Rightarrow x=\frac{k\pi }{2}+\frac{\pi }{8},k\in Z$  $x\in \left[ -\pi ,\frac{3\pi }{2} \right]\Rightarrow -\pi \le x\le \frac{3\pi }{2}\Rightarrow -\pi \le \frac{k\pi }{2}+\frac{\pi }{8}\le \frac{3\pi }{2}\xrightarrow{\times \frac{8}{\pi }}-8\le 4k+1\le 12\Rightarrow -9\le 4k\le 11\Rightarrow -\frac{9}{4}\le k\le \frac{11}{4}\xrightarrow{k\in Z}k\in \left\{ -2,-1,0,1,2 \right\}$