$x^{2}$ - 4x +3 $\geq$ 0
<=> $x^{2}$ -3x-x +3 $\geq$ 0
<=> x(x-1 )-3 (x-1)$\geq$ 0
<=> (x-1) (x-3)$\geq$ 0
<=> +) $\left \{ {{x-1 \geq 0} \atop {x-3 \geq}0} \right.$
+) $\left \{ {{x-1\leq 0} \atop {x-3\leq 0}} \right.$
<=> +) $\left \{ {{x\geq 1} \atop {x\geq 3}} \right.$
+) $\left \{ {{x\leq1} \atop {x\leq 3}} \right.$
<=> +) x$\geq$ 3
+) x$\leq$ 1
Vậy...................