Question

(x² - 36)(x² - 81) ≤ 0

Answer 1

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x^2-36\ge0\\x^2-81\le0\end{matrix}\right.\\\left\{{}\begin{matrix}x^2-36\le0\\x^2-81\ge0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow36\le x^2\le81\\ \Leftrightarrow-6\le x\le9\)

Answer 2

x \(\in\) { 6 ; 9 }