Объяснение:

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[tex]\displaystyle\bf\\x-\frac{1}{x} =-6\\\\\\x^{3} -\frac{1}{x^{3} } =x^{3} -\Big(\frac{1}{x} \Big)^{3} =\underbrace{\Big(x-\frac{1}{x} \Big)}_{-6}\cdot\Big[x^{2} +x\cdot \frac{1}{x} +\Big(\frac{1}{x} \Big)^{2} \Big]=\\\\\\=-6\cdot\Big[x^{2} +1+\Big(\frac{1}{x} \Big)^{2} \Big]=-6\cdot\Big[\Big(x-\frac{1}{x} \Big)^{2} +3\Big]=\\\\\\=-6\cdot\Big((-6)^{2} +3\Big)=-6\cdot(36+3)=-6\cdot39=-234\\\\\\Otvet \ : \ -234[/tex]