\[\begin{array}{l} {\text{Докажите тождество:}} \hfill \\ \sqrt[8]{{\frac{{3 + 2\sqrt[4]{2}}}{{3 - 2\sqrt[4]{2}}}}} + \sqrt[8]{{\frac{{3 - 2\sqrt[4]{2}}}{{3 + 2\sqrt[4]{2}}}}} = \frac{1}{7}\sqrt {98 + 14\sqrt {35 + 21\sqrt 2 } } . \hfill \\ \end{array}\]