已知函数\(f(x)=ax- \dfrac{b}{x}-2\ln x\),\(f(1)=0\).
\((1)\)若函数\(f(x)\)在其定义域内为单调函数,求实数\(a\)的取值范围?
\((2)\)若函数\(f(x)\)的图像在\(x=1\)处的切线的斜率为\(0\),且\(a_{n+1}=f′\left( \left. \dfrac{1}{a_{n}+1} \right. \right)-na_{n}+1\),若\(a_{1}\geqslant 3\),求证:\(a_{n}\geqslant n+2\).