[tex] z^{3} = (a+ib)^{3}, (a +ib)^{3}= a^{3} + 3a^{2}ib- 3ab^{2}- ib^{3}
z (conjugat) = a-ib
a^{3} + 3a^{2}ib- 3ab^{2}- ib^{3} = a-ib =\ \textgreater \ \left \{ {{a( a^{2}- 3b^{2}) =a} \atop { ib(3a^{2}- b^{2} ) =-ib}} \right. =\ \textgreater \ \left \{ {{ a^{2}-3 b^{2} =1} \atop { 3a^{2}- b^{2} =-1}} \right.
De aici simiplifici cu -3 unde vrei...
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