9.
\((1)\)若\(\tan α=-2\),且\(\sin α < 0\),则\(\cos α= \)____________.
\((2)\)已知\(\sin (α- \dfrac{π}{4})= \dfrac{3}{5} \)则\(\cos (α+ \dfrac{π}{4}) \)的值为
\((3)\)函数\(y= \sqrt{1-2\cos x} \)的定义域为____________.
\((4)\)关于函数\(f(x)=|\sin 2x|\)有下列命题:
\(①\)函数\(f(x)\)的最小正周期为\(π\);
\(②\)函数\(f(x)\)在区间\((0, \dfrac{π}{2} )\)上单调递增;
\(③\)函数\(f(x)\)的对称轴是\(x= \dfrac{kπ}{2}+ \dfrac{π}{4},k∈Z \);
\(④\)若\(f(x_{1})=f(x_{2})=1\),则\(|{x}_{1}-{x}_{2}{|}_{min}= \dfrac{π}{6} \);
其中正确的序号为