8.
\((\)一\()\)在直角坐标系\(xOy\)中,直线\(l\)的参数方程为:\(\begin{cases} x=1+t\cos \theta \\ y=\sqrt{3}+t\sin \theta \end{cases},t\)为参数,\(\theta \in \left[ 0,\pi \right).\)以坐标原点为极点,以\(x\)轴的正半轴为极轴,建立极坐标系,圆\(C\)的极坐标方程为:\(\rho =8\sin (\theta +\dfrac{\pi }{6})\).
\((1)\)在直角坐标系\(xOy\)中,求圆\(C\)的圆心的直角坐标;
\((2)\)设点\(P(1,\sqrt{3})\),若直线\(l\)与圆\(C\)交于\(A,B\)两点,求证:\(\left| PA \right|\cdot \left| PB \right|\)为定值,并求出该定值.
\((\)二\()\)设函数\(f(x)=\left| x+1 \right|+\left| x-a \right|.(x\in R)\)
\((1)\) 当\(a=2\)时,求不等式\(f(x) > 5\)的解集;
\((2)\)对任意实数\(x\),都有\(f(x)\geqslant 3\)恒成立,求实数\(a\)的取值范围.