9．
若函数\(f\)\((\)\(x\)\()\)同时满足：\(①\)对于定义域上的任意\(x\)，恒有\(f\)\((\)\(x\)\()+\)\(f\)\((-\)\(x\)\()=0\)；\(②\)对于定义域上的任意\(x\)\({\,\!}_{1}\)，\(x\)\({\,\!}_{2}\)，当\(x\)\({\,\!}_{1}\neq \)\(x\)\({\,\!}_{2}\)时，恒有\( \dfrac{f(x_{1})-f(x_{2})}{x_{1}-x_{2}} < 0.\)则称函数\(f\)\((\)\(x\)\()\)为“理想函数”\(.\)给出下列三个函数中：\((1)\)\(f\)\((\)\(x\)\()= \dfrac{1}{x}\)；\((2)\)\(f\)\((\)\(x\)\()=\)\(x\)\({\,\!}^{2}\)；\((3)\)\(f\)\((\)\(x\)\()=\begin{cases}-x^{2},x\geqslant 0, \\ x^{2},x < 0.\end{cases}\)能被称为“理想函数”的有________\((\)填相应的序号\()\)．