$\begin{array}{1 1}(a)\;(-\infty,3-2\sqrt 2)\\(b)\;(3-2\sqrt 2,3+2\sqrt 2)\\(c)\;(-\infty,3-2\sqrt 2)\cup (3+2\sqrt 2,\infty)\\(d)\;None\;of\;the\;above\end{array}$