3.
\((1)\)设\(A{=}\{ x{|}x^{2}{-}8x{+}15{=}0\}{,}B{=}\{ x{|}ax{-}1{=}0\}\),若\(B{⊆}A\),则实数\(a\)组成的集合\(C{=}\) ______ .
\((2)\)函数\(f(x){=}\begin{cases} ax^{2}{+}x{-}1(x{ > }2) \\ {-}x{+}1(x{\leqslant }2) \end{cases}\)是\(R\)上的单调递减函数,则实数\(a\)的取值范围是______ .
\((3)\)已知函数\(f(x)\)是定义在\(R\)上的奇函数,且当\(x{ > }0\)时,\(f(x){=}2^{x}{-}1\),则\(f(f({-}1))\)的值为______ .
\((4)\)直线\(l{:}\begin{cases} x{=}t\cos\alpha \\ y{=}t\sin\alpha \end{cases}\ (t\)为参数\()\)与圆\(C\):\((x{+}6)^{2}{+}y^{2}{=}25\)交于\(A{,}B\)两点,且\({|}AB{|} = \sqrt{10}\),则直线\(l\)的斜率为______ .