Réponse :
Bonjour,
a. (3x + 1)(x-9) = 0, si 3x + 1 = 0 ou si x-9 = 0
Pour 3x + 1 = 0
= 3x + 1 - 1 = 0 - 1, (On soustrait 1 des deux côtés)
= 3x = -1
= (3x) / 3 = -1 / 3, (On divise par 3 des deux côtés)
= x = -1 / 3
Pour x-9 = 0
= x - 9 + 9 = 0 + 9, (On additionne par 9 des deux côtés)
= x = 9
L'équation (3x + 1)(x-9) = 0 admet deux solutions :
x = -1/3 et x = 9
b. (6x +7)(4x - 11) = 0, si 6x +7 = 0 ou si 4x - 11 = 0
Pour 6x +7 = 0
= 6x +7 - 7 = 0 - 7
= 6x = -7
= (6x) / 6 = -7 / 6
= x = -7 / 6
Pour 4x - 11 = 0
= 4x - 11 + 11 = 0 + 11
= 4x = 11
= (4x) / 4 = 11 / 4
= x = 11 / 4
L'équation (6x +7)(4x - 11) = 0 admet deux solutions :
x = -7 / 6 et x = 11 / 4
c. (9x - 3)(- 5x - 13) = 0, si 9x - 3 = 0 ou si -5x - 13 = 0
Pour 9x - 3 = 0
= 9x - 3 + 3 = 0 + 3
= 9x = 3
= (9x) / 9 = 3 / 9 = 1 / 3
= x = 1 / 3
Pour -5x - 13 = 0
= -5x - 13 + 13 = 0 + 13
= -5x = 13
= (-5x) / 5 = 13 / 5
= -x = 13 / 5
= x = - 13 / 5
L'équation (6x +7)(4x - 11) = 0 admet deux solutions :
x = 1 / 3 et x = - 13 / 5
