6.
\((1)\)已知\(y\)\(=\)\(f\)\((\)\(x\)\()\)是一次函数,且有\(f\)\([\)\(f\)\((\)\(x\)\()]=16\)\(x\)\(-15\), 则\(f\)\((\)\(x\)\()\)的解析式为 _____________________.
\((2)\)若函数\(f\left( x \right)=\dfrac{\left( x+1 \right)\left( x+a \right)}{x}\)是奇函数,则实数\(a=\) __________.
\((3)\)已知函数\(f\left( x \right)=x+\sqrt{2x-1}\),则\(f\left( x \right)\)的最小值为 ___________.
\((4)\)若集合\(A=\left\{ x|a{{x}^{2}}+3x+2=0 \right\}\)中至多有\(1\)个元素, 则实数\(a\)的取值范围为 ________________.