$\operatorname{Sin}(\pi +x)=-\operatorname{Sin}x,\operatorname{Cos}(\frac{\pi }{2}+x)=-\operatorname{Sin}x,\operatorname{Sin}(\pi -x)=\operatorname{Sin}x$ $\Rightarrow (-\operatorname{Sin}x)(-\operatorname{Sin}x)-2\operatorname{Sin}x=1=0\Rightarrow {{\operatorname{Sin}}^{2}}x-2\operatorname{Sin}x+1=0\Rightarrow {{(\operatorname{Sin}x-1)}^{2}}=0$ $\Rightarrow \operatorname{Sin}x-1=0\Rightarrow \operatorname{Sin}x=1\to x=2k\pi =\frac{\pi }{2}$