There are no real number solutions to this, just complex ones:
$${{\mathtt{x}}}^{{\mathtt{4}}}{\mathtt{\,-\,}}{\mathtt{15}}{\mathtt{\,\times\,}}{{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{64}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = {\mathtt{\,-\,}}{\frac{{\sqrt{{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,\small\textbf+\,}}{\mathtt{15}}}}}{{\sqrt{{\mathtt{2}}}}}}\\
{\mathtt{x}} = {\frac{{\sqrt{{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,\small\textbf+\,}}{\mathtt{15}}}}}{{\sqrt{{\mathtt{2}}}}}}\\
{\mathtt{x}} = {\mathtt{\,-\,}}{\frac{{\sqrt{{\mathtt{15}}{\mathtt{\,-\,}}{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}}}}{{\sqrt{{\mathtt{2}}}}}}\\
{\mathtt{x}} = {\frac{{\sqrt{{\mathtt{15}}{\mathtt{\,-\,}}{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}}}}{{\sqrt{{\mathtt{2}}}}}}\\
\end{array} \right\}$$
.
There are no real number solutions to this, just complex ones:
$${{\mathtt{x}}}^{{\mathtt{4}}}{\mathtt{\,-\,}}{\mathtt{15}}{\mathtt{\,\times\,}}{{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{64}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = {\mathtt{\,-\,}}{\frac{{\sqrt{{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,\small\textbf+\,}}{\mathtt{15}}}}}{{\sqrt{{\mathtt{2}}}}}}\\
{\mathtt{x}} = {\frac{{\sqrt{{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}{\mathtt{\,\small\textbf+\,}}{\mathtt{15}}}}}{{\sqrt{{\mathtt{2}}}}}}\\
{\mathtt{x}} = {\mathtt{\,-\,}}{\frac{{\sqrt{{\mathtt{15}}{\mathtt{\,-\,}}{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}}}}{{\sqrt{{\mathtt{2}}}}}}\\
{\mathtt{x}} = {\frac{{\sqrt{{\mathtt{15}}{\mathtt{\,-\,}}{\sqrt{{\mathtt{31}}}}{\mathtt{\,\times\,}}{i}}}}{{\sqrt{{\mathtt{2}}}}}}\\
\end{array} \right\}$$
.