I'm \,\, going \,\, to \,\, assume \,\, it's \,\, z^{3}=\frac{1+i}{\sqrt{2}} \,\, because \,\, this \,\, expression \,\, yields \,\, workable \,\, values. \\\\ z^{3}=\frac{1+i}{\sqrt{2}}=cis\left ( \frac{\pi}{4} \right ) \\\\ z = cis\left ( \frac{\pi}{12}+\frac{2k\pi}{3} \right ), \,\, k=0,\pm 1...