3.
如图,在平面直角坐标系\(xOy\)中,焦点在\(x\)轴上的椭圆\(C:\dfrac{x^{2}}{8}+\dfrac{y^{2}}{b^{2}}=1\)经过点\((b,2e)(\)其中\(e\)为椭圆\(C\)的离心率\()\),过点\(T(1,0)\)作斜率为\(k(k > 0)\)的直线\(l\)交椭圆\(C\)于\(A\),\(B\)两点\((A\)在\(x\)轴下方\()\).
\((1)\) 求椭圆\(C\)的标准方程\(;\)
\((2)\) 设过点\(O\)且平行于\(l\)的直线交椭圆\(C\)于点\(M\),\(N\),求\(\dfrac{{AT}\mathrm{{·}}{BT}}{MN^{2}}\)的值\(;\)
\((3)\) 记直线\(l\)与\(y\)轴的交点为\(P\),若\(\overrightarrow{{AP}}=\dfrac{2}{5}\overrightarrow{{TB}}\),求直线\(l\)的斜率\(k\).