ĐK: \(\left\{{}\begin{matrix}x-4\ge0\\x^2-9>0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ge4\\x^2>9\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ge4\\\left[{}\begin{matrix}x>3\\x< -3\end{matrix}\right.\end{matrix}\right.\) \(\Leftrightarrow x\ge4\)
TXĐ: D = [4;+∞)