Ta có [tex]x^2-2x-3\geq 0[/tex]
[tex]\Leftrightarrow x^2-2x+1-4\geq 0[/tex]
[tex]\Leftrightarrow (x-1)^2-2^2\geq 0[/tex]
[tex]\Leftrightarrow (x-1-2)(x-1+2)\geq 0[/tex]
[tex]\Leftrightarrow (x-3)(x+1)\geq 0[/tex]
Nên
Hoặc
[tex]\left\{\begin{matrix} x-3\geq 0 & \\ x+1\geq 0 & \end{matrix}\right.[/tex]
[tex]\Leftrightarrow \left\{\begin{matrix} x\geq 3 & \\ x\geq -1& \end{matrix}\right.[/tex]
[tex]\Rightarrow x\geq 3[/tex]
Hoặc
[tex]\left\{\begin{matrix} x-3\leq 0 & \\ x+1\leq 0 & \end{matrix}\right.[/tex]
[tex]\Leftrightarrow \left\{\begin{matrix} x\leq 3 & \\ x\leq -1& \end{matrix}\right.[/tex]
[tex]\Rightarrow x\leq -1[/tex]
Vậy [tex]x\geq 3;x\leq -1[/tex]