$\begin{array}{*{35}{l}}
\text{ }\!\!~\!\!\text{ } & \sin \left( x+\frac{\pi }{4} \right)=\frac{3}{2\sqrt{2}}\cos x-\frac{\sqrt{3}}{2\sqrt{2}}\sin x\xrightarrow{\times \sqrt{2}}\sqrt{2}\sin \left( x+\frac{\pi }{4} \right)=\frac{3}{2}\cos x-\frac{\sqrt{3}}{2}\sin x \\
\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ } & \to \sin x+\cos x=\cos x+\frac{1}{2}\cos x-\frac{\sqrt{3}}{2}\sin x\to \sin x=\cos \left( \frac{\pi }{3}+x \right)=\sin \left( \frac{\pi }{2}-\frac{\pi }{3}-x \right) \\
\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ } & \sin x=\sin \left( \frac{\pi }{6}-x \right)\to x=2k\pi +\frac{\pi }{6}-x\to x=k\pi +\frac{\pi }{12} \\
\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ } & \to x=\frac{\pi }{12},-\pi +\frac{\pi }{12}\to \overline{x}=\frac{\frac{\pi }{12}-\pi +\frac{\pi }{12}}{2}=-\frac{5\pi }{12} \\
\text{ }\!\!~\!\!\text{ } & {} \\
\end{array}$