`a, x^2 - 6x + 9 < x^2 - 5x + 4`
`<=> (x^2 - x^2) + (-6x + 5x) + (9-4) < 0`
` <=> 5 - x < 0`
`<=> x > 5`.
`b, x^2 - 4x + 3 >=0`
`=> (x-1)(x-3) >=0`
`TH_1 {(x-1 >=0), (x-3>0):}`
`=> {(x>=1),(x>3):}`
`=> x >=1`.
`TH_2: {(x-1 <=0), (x-3) <0:}`
`=> {(x <= 1), (x < 3):}`
`=> x < 3``
a) `(x-3)^2 < x^2 -5x +4`
`<=>x^2 -6x +9 < x^2 -5x +4`
`<=> x^2 -6x +9 - x^2 +5x -4 <0`
`<=> -x +5 <0`
`<=> -x < -5`
`<=> x >5`
Vậy `S = {x|x>5}`
b)`x^2 -4x +3>=0`
`<=>(x-3)(x-1)>=0`
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-3>0\\x-1\ge0\end{matrix}\right.\\\left\{{}\begin{matrix}x-3\ge0\\x-1>0\end{matrix}\right.\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>3\\x\ge1\end{matrix}\right.\\\left\{{}\begin{matrix}x< 3\\x\le1\end{matrix}\right.\end{matrix}\right.\)
