\(1,\left[{}\begin{matrix}\left\{{}\begin{matrix}x-6\ge0\\x-2>0\end{matrix}\right.\\\left\{{}\begin{matrix}x-6\le0\\x-2< 0\end{matrix}\right.\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x\ge6\\x< 2\end{matrix}\right.\\ 2,4-9x^2\ge0\\ \Leftrightarrow-\dfrac{2}{3}\le x\le\dfrac{2}{3}\)
\(3,x^2-8x-9\ge0\\ \Leftrightarrow\left(x+1\right)\left(x-9\right)\ge0\Leftrightarrow\left[{}\begin{matrix}x\ge9\\x\le-1\end{matrix}\right.\)
1: ĐKXĐ: (x-6)/(x-2)>=0
=>x>=6 hoặc x<2
2: ĐKXĐ: 4-9x^2>=0
=>9x^2<=4
=>x^2<=4/9
=>-2/3<=x<=2/3
3: ĐKXĐ: x^2-8x-9>=0
=>(x-9)(x+1)>=0
=>x>=9 hoặc x<=-1
