Đặt \(\left\{{}\begin{matrix}\sqrt[3]{x+1}=a\\\sqrt[3]{3x+1}=b\end{matrix}\right.\)
\(\Rightarrow a+b+\sqrt[3]{a^3+b^3}=0\Leftrightarrow a+b=-\sqrt[3]{a^3+b^3}\)
\(\Leftrightarrow\left(a+b\right)^3=-\left(a+b\right)\left(a^2-ab+b^2\right)\)
\(\Leftrightarrow\left(a+b\right)\left(2a^2+2b^2+ab\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}a=-b\\a=b=0\left(vn\right)\end{matrix}\right.\)
\(\Rightarrow x+1=-\left(3x+1\right)\)
\(\Rightarrow x=-\frac{1}{2}\)