Câu 13:
1: Ta có: \(\sqrt[3]{1000x}-\sqrt[3]{64x}-\sqrt[3]{27x}=15\)
\(\Leftrightarrow10\cdot\sqrt[3]{x}-4\cdot\sqrt[3]{x}-3\cdot\sqrt[3]{x}=15\)
\(\Leftrightarrow3\cdot\sqrt[3]{x}=15\)
\(\Leftrightarrow x=125\)
2) Ta có: \(\sqrt[3]{x-3}+3=x\)
\(\Leftrightarrow\sqrt[3]{x-3}=x-3\)
\(\Leftrightarrow x-3=\left(x-3\right)^3\)
\(\Leftrightarrow\left(x-3\right)^3-\left(x-3\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left(x-2\right)\left(x-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=2\\x=4\end{matrix}\right.\)
Câu 12:
Ta có: \(\sqrt[3]{x+7}-3=1\)
\(\Leftrightarrow\sqrt[3]{x+7}=4\)
\(\Leftrightarrow x+7=64\)
hay x=57
