23. `x(x+2) ≥ 0`
`<=> x ≥ 0 ; x ≤ -2`
24. `x^2 - 5x + 6 ≥ 0`
`<=> x ≥ 3; x ≤ 2`
27. `4-|x| ≥ 0`
`<=> |x| ≤ 4`
`<=> x \in {\pm1 ; \pm2;\pm3}`
28. `x-2\sqrt(x-1) ≥ 0`
`<=> x ≥ 2\sqrt(x-1)`
`=> x^2 ≥ 4(x-1) (x≥1)`
`<=> x ≥ 1`
25. `|x| - 1≥ 0`
`<=> |x| ≥ 1`
`<=> x \ne 0`
26. `|x-1| - 3≥ 0`
`<=> |x-1| ≥ 3`
`<=>` \(\left[ \begin{array}{l}x-1≥3\\x-1≤-3\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x≥4\\x≤-2\end{array} \right.\)
21. `x^2 - 3≥ 0`
`<=> x ≤ -\sqrt3 ; x≥ \sqrt3`
22. `x^2 - 2x-3 ≥ 0`
`<=> x ≤ -1 ; 3 ≤ x`
