7: ĐKXĐ: \(x^2-3x+2>=0\)
=>(x-1)(x-2)>=0
TH1: \(\left\{{}\begin{matrix}x-1>=0\\x-2>=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>=1\\x>=2\end{matrix}\right.\)
=>x>=2
TH2: \(\left\{{}\begin{matrix}x-1< =0\\x-2< =0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x< =1\\x< =2\end{matrix}\right.\)
=>x<=1
9: ĐKXĐ: \(9x^2-6x+1>=0\)
=>\(\left(3x-1\right)^2>=0\)(luôn đúng)
=>\(x\in R\)
8: ĐKXĐ: \(x^2+4x+5>=0\)
=>\(x^2+4x+4+1>=0\)
=>\(\left(x+2\right)^2+1>=0\)(luôn đúng)
=>\(x\in R\)
7) ĐKXĐ:\(x^2-3x+2\ge0\)
\(\Leftrightarrow\left(x-1\right)\left(x-2\right)\ge0\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-1\ge0\\x-2\ge0\end{matrix}\right.\\\left\{{}\begin{matrix}x-1\le0\\x-2\le0\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x\ge1\\x\ge2\end{matrix}\right.\\\left\{{}\begin{matrix}x\le1\\x\le2\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow x\ge2\) hoặc \(x\le1\)
