Question

1. Tìm x \(\in\) Q biết :

1. \(\left(1-2x\right)^4\) = 81

Answer 1

\(\left(1-2x\right)^4=81\Leftrightarrow\left[{}\begin{matrix}1-2x=\sqrt[4]{81}\\1-2x=-\sqrt[4]{81}\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}1-2x=3\\1-2x=-3\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}2x=1-3\\2x=1+3\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}2x=-2\\2x=4\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=2\end{matrix}\right.\) vậy \(x=-1;x=2\)