a: =>-4x<=1
=>x>=-1/4
b: =>9x>-1
=>x>-1/9
c: TH1: x-3>=0; 5-x<=0
=>x>=3 và x>=5
=>x>=5
TH2: x-3<=0
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-3\right)^2>=\left(5-x\right)^2\\x< =3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x^2-6x+9>=x^2-10x+25\\x< =3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}4x< =16\\x< =3\end{matrix}\right.\Leftrightarrow x< =3\)
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