\((\)本小题满分\(12\)分\()\)
设函数\(f_{n}\)\((\)\(x\)\()=\)\(x^{n}\)\(+\)\(bx\)\(+\)\(c\)\((\)\(n\)\(∈N_{+}\),\(b\),\(c\)\(∈R)\).
\((1)\)设\(n\)\(\geqslant 2\),\(b\)\(=1\),\(c\)\(=-1\),证明:\(f_{n}\)\((\)\(x\)\()\)在区间 内存在唯一的零点;
\((2)\)设\(n\)\(=2\),若对任意\(x\)\({\,\!}_{1}\),\(x\)\({\,\!}_{2}\) \([-1,1]\),有 ,求\(b\)的取值范围;
\((3)\)在\((1)\)的条件下,设\(x_{n}\)是\(f_{n}\)\((\)\(x\)\()\)在 内的零点,判断数列\(x\)\({\,\!}_{2}\),\(x\)\({\,\!}_{3}\),\(…\),\(x_{n}\),\(…\)的增减性.