Tìm x, biết: |2x - 5| = 4.

Ta có: |2x - 5| = 4.

∙ Nếu 2x - 5 ≥ 0 hay $x\ge \frac{5}{2}$  ta có:

2x – 5 = 4.

2x = 9

 $x=\frac{9}{2}$(thỏa mãn)

∙ Nếu 2x - 5 < 0 hay $x<\frac{5}{2}$  ta có:

2x – 5 = -4

2x = 5 - 4

2x = 1

 $x=\frac{1}{2}$(thỏa mãn)

Vậy $x\in \left\{\frac{9}{2};\frac{1}{2}\right\}$ .