Réponse :
Explications étape par étape
1 /x² + 4 = 3x + 14
⇔ x² - 3x + 4 - 14 = 0
⇔ x² - 3x - 10 = 0
Factorisation
x² - 3x - 10 = 0
⇔ x² - 5x + 2x - 10 = 0
⇔ x ( x - 5 ) + 2 ( x - 5 ) = 0
⇔ ( x - 5 ) ( x + 2 ) = 0
x - 5 = 0 ou x + 2 = 0
⇔ x = 5 ⇔ x = -2
S = { -2 ; 5 }
2/a 3x - 1 = -5
⇔ 3x = -4
⇔ x = - 4/3
b 7x + 2 = 4x - 9
⇔ 7x - 4x = -9 - 2
⇔ 3x = -11
⇔ x = - 11/3
c/ 7/4 x = 5/3
⇔ x = ( 5/3 ) / ( 7/4 )
⇔ x = 5/3 * 4/7
⇔ x = 20/21
3 / ( 5x - 2 ) ( 6 - 2x ) = 0
Il suffit que :
5x - 2 = 0 ou 6 - 2x = 0
⇔ 5x = 2 ⇔ -2x = - 6
⇔ x = 2/5 ⇔ x = 3
S = { 2/5 ; 3 }
