8.
如图,已知线段\(AE\),\(BF\)为抛物线\(C:{{x}^{2}}=2py\left( p > 0 \right)\)的两条弦,点\(E\)、\(F\)不重合\(.\)函数\(y={a}^{x}(a > 0且a\neq 1) \)的图象所恒过的定点为抛物线\(C\)的焦点.
\((I)\)求抛物线\(C\)的方程;
\((\)Ⅱ\()\)已知\(A(2,1),B(-1,\dfrac{1}{4})\),直线\(AE\)与\(BF\)的斜率互为相反数,且\(A\),\(B\)两点在直线\(EF\)的两侧.
\(①\)问直线\(EF\)的斜率是否为定值\(?\)若是,求出该定值;若不是,请说明理由.
\(②\)求\(\overrightarrow{OE}\cdot \overrightarrow{OF}\)的取值范围.