October 16, 2009

Solve $\sqrt[3]{13x+37} - \sqrt[3]{13x-37}=\sqrt[3]{2}$.

Solution.   Cubing both sides yields
\begin{gathered} (13x+37) -3\sqrt[3]{13x+37}\cdot\sqrt[3]{13x-37}\left(\sqrt[3]{13x+37}-\sqrt[3]{13x-37}\right) - (13x-37)=2 \\ \Longrightarrow 74 -3\sqrt[3]{13x+37}\cdot\sqrt[3]{13x-37}(\sqrt[3]{2}) = 2 \\ \Longrightarrow (\sqrt[3]{2})\left(\sqrt[3]{169x^2-1369}\right) = 24 \end{gathered}
Cubing once more gives $2(169x^2-1369) = 13,824 \Longrightarrow 169x^2 - 8281 = 0$, so that $x=\pm 7$. Both of these solutions work in the original equation.