Bonsoir.
5x + 1 = 11
⇔ 5x = 11 - 1
⇔ x = 10/5
⇔ x = 2
4x - 9 = 2x - 3
⇔ 4x - 2x = - 3 + 9
⇔ 2x = 6
⇔ x = 6/2
⇔ x = 3
(x - 5)(2x + 8) = 0
⇔ x - 5 = 0 soit x = 5
et 2x + 8 = 0 soit 2x = - 8 ⇔ x = -8/2 = - 4
x² = 21 donc x = [tex]\sqrt{21\\}[/tex] et x = - [tex]\sqrt{21\\}[/tex]
Bonne soirée !
