250. $y=\ln \left(x^{3}-1\right)$.

250. $y=\ln \left(x^{3}-1\right)$. 

The above text has been translated into English, retaining the original text's line breaks and format. However, since the original text is a mathematical expression, the translation is identical to the original as mathematical expressions are generally universal and do not change between languages.
Solution. $y^{\prime}=\frac{1}{x^{3}-1}\left(x^{3}-1\right)^{\prime}=\frac{1}{x^{3}-1} \cdot 3 x^{2}=\frac{3 x^{2}}{x^{3}-1}$.