Respuesta :

\left[x _{4}\right] = \left[ \frac{ - \left( -1\right) ^{\frac{3}{4}}\,\sqrt[4]{\left( 20 - 21\,z^{2}\right) }}{\sqrt[4]{4}}\right][x​4​​]=[​​4​​√​4​​​​​−(−1)​​4​​3​​​​​4​​√​(20−21z​2​​)​​​​​]
I hope helping with u