Монгол Бодлогын Сан

Заавар: $$a^3-b^3=(a-b)^3+3ab(a-b)$$

Бодолт: $$x^3-\displaystyle\frac{1}{x^3}=\left(x-\displaystyle\frac{1}{x}\right)^3+3\cdot x\cdot\dfrac1x\cdot\left(x-\displaystyle\frac{1}{x}\right)=$$ $$=\left(x-\displaystyle\frac{1}{x}\right)^3+3\cdot \left(x-\displaystyle\frac{1}{x}\right)=2^3+3\cdot 2=14$$