\((1)\)已知向量\(\overrightarrow{a},\overrightarrow{b}\)的夹角为\(60^{\circ}\),\(\left| \overrightarrow{a} \right|=2,\left| \overrightarrow{b} \right|=1\),则\(\left| \overrightarrow{a}+2\overrightarrow{b} \right|=\)_____.
\((2)\)已知双曲线\(C\):\(\dfrac{{{x}^{2}}}{{{a}^{2}}}-\dfrac{{{y}^{2}}}{{{b}^{2}}}=1(a > 0,b > 0)\)的右顶点为\(A\),以\(A\)为圆心,\(b\)为半径作圆\(A\),圆\(A\)与双曲线\(C\)的一条渐近线交于\(M\),\(N\)两点\(.\)若\(∠MAN=60^{\circ}\),则\(C\)的离心率为_____.
\((3)\)在\(\triangle ABC\)中,\(AB\)边上的中线\(CO=4\),若动点\(P\)满足\(\overrightarrow{PA}={{\sin }^{2}}\dfrac{\theta }{2}\overrightarrow{OA}+{{\cos }^{2}}\dfrac{\theta }{2}\overrightarrow{CA}(\theta \in R)\),则\((\overrightarrow{PA}+\overrightarrow{PB})\cdot \overrightarrow{PC}\)的最小值是 .
\((4)\)如图,圆形纸片的圆心为\(O\),半径为\(5 cm\),该纸片上的等边三角形\(ABC\)的中心为\(O\).\(D\),\(E\),\(F\)为圆\(O\)上的点,\(\triangle DBC\),\(\triangle ECA\),\(\triangle FAB\)分别是以\(BC\),\(CA\),\(AB\)为底边的等腰三角形\(.\)沿虚线剪开后,分别以\(BC\),\(CA\),\(AB\)为折痕折起\(\triangle DBC\),\(\triangle ECA\),\(\triangle FAB\),使得\(D\),\(E\),\(F\)重合,得到三棱锥\(.\)当\(\triangle ABC\)的边长变化时,所得三棱锥体积\((\)单位:\(cm\)\({\,\!}^{3}\)\()\)的最大值为_____.