Question

What substation should be used to rewrite 4x^4-21z^2+20=0

Answer 1

\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​​)​​​​​]
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