1.
\((1)\)求圆心为\(\left( 2,-1 \right)\)且与\(x\)轴相切的圆的标准方程_______.
\((2)\)已知\(f(x)=\log _{a}^{{}}(8-3ax)\)在\([-1,2]\)上的减函数,则实数\(a\)的取值范围是_______.
\((3)\)已知直线\(ax+by=1\)与圆\({{x}^{2}}+{{y}^{2}}=\dfrac{1}{4}\)相交于不同的\(A,B\)两点,且\(\left| AB \right| < \dfrac{\sqrt{2}}{2}\),则\({{a}^{2}}+{{b}^{2}}-2a\)的取值范围为_______.
\((4)\)已知函数\(f(x)={{x}^{2}}+2x\),\(g(x)={{(\dfrac{1}{2})}^{x}}+m\),若任意\({{x}_{1}}\in [1,2]\),存在\({{x}_{2}}\in [-1,1]\),使得\(f({{x}_{1}})\geqslant g({{x}_{2}})\),则实数\(m\)的取值范围是______________\(.\)