Chứng minh :
$\frac{{\sqrt[3]{{a + \sqrt {2 - {a^2}} }}.\sqrt[6]{{1 - a\sqrt {2 - {a^2}}
}}}}{{\sqrt[3]{{1 - {a^2}}}}} =\begin{cases}\sqrt[6]{2}\,\,\,\,\,nếu\,\,\,\,\,\left| a \right| < 1 \\ - \sqrt[6]{2}\,\,\,\,\,\,nếu\,\,\,\,\,1 < \left| a \right| \le 2 \end{cases} $
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