4.
已知复数\(z_{1}=\sin x+λi\),\(z_{2}=(\sin x+ \sqrt {3}\cos x)-i(λ,x∈R,i\)为虚数单位\()\).
\((1)\)若\(2z_{1}=z_{2}i\),且\(x∈(0,π)\),求\(x\)与\(λ\)的值;
\((2)\)设复数\(z_{1}\),\(z_{2}\)在复平面上对应的向量分别为\( \overrightarrow{OZ_{1}}, \overrightarrow{OZ_{2}}\),若\( \overrightarrow{OZ_{1}}⊥ \overrightarrow{OZ_{2}}\),且\(λ=f(x)\),求\(f(x)\)的最小正周期和单调递减区间.