8.
\((1)\)命题“\(\forall x\in R\),\({{x}^{2}}+4x+5 > 0\)”的否定是 .
\((2).\)已知直线\(l:2x-y-2=0\)与抛物线\(C:{{y}^{2}}=8x\)交于\(A\),\(B\)两点,则\(\left| AB \right|=\) .
\((3).\)已知实数\(a,b,c\in R\),则“\(a > b\)”是“\(a{{c}^{2}} > b{{c}^{2}}\)”的 条件.
\((4).\)若椭圆\(\dfrac{{{x}^{2}}}{{{a}^{2}}}+\dfrac{{{y}^{2}}}{{{b}^{2}}}=1(a > b > 0)\)离心率为\(\dfrac{\sqrt{2}}{2}\),则双曲线\(\dfrac{{{x}^{2}}}{{{a}^{2}}}-\dfrac{{{y}^{2}}}{{{b}^{2}}}=1\)的离心率为 .
\((5).\)已知椭圆\(C\)的方程为\(\dfrac{{{x}^{2}}}{{{a}^{2}}}+\dfrac{{{y}^{2}}}{{{b}^{2}}}=1\left( a > b > 0 \right),{{F}_{1}},{{F}_{2}}\)为其左、右焦点,\(e\)为离心率,\(P\)为椭圆上一动点,则有如下命题:
\(①\)当\(0 < e < \dfrac{\sqrt{2}}{2}\)时,使\(\Delta P{{F}_{1}}{{F}_{2}}\)为直角三角形的点\(P\)有且只有\(4\)个;
\(②\)当\(e=\dfrac{\sqrt{2}}{2}\)时,使\(\Delta P{{F}_{1}}{{F}_{2}}\)为直角三角形的点\(P\)有且只有\(6\)个;
\(③\)当\(\dfrac{\sqrt{2}}{2} < e < 1\)时,使\(\Delta P{{F}_{1}}{{F}_{2}}\)为直角三角形的点\(P\)有且只有\(8\)个.
其中真命题的有 \((\)请写出所有真命题的序号\()\).