Réponse :
Explications étape par étape
Bsr,
1)
(2x+3) ² = 4x² +12x + 9
(2x+3)(5x-7) = 10x²-14x +15x -21
4x² +12x + 9+ 10x²-14x +15x -21= 14x² +13x-12
2)
(2x+3)(2x+3 + 5x-7) = (2x+3) ( 7x -4)
3)
(2x+3) ( 7x-4) = 0
2 solutions
2x+3 = 0
2x= -3
x = -3/2
ou
7x-4 = 0
7x = 4
x = 4/7
4)
x= -3/2
14x² +13x-12
14 *(-3/2)² + 13(-3/2) -12 =
14* 9/4 - 39/2 -12 =
126/4 - 78/4 - 48/4= 0
☺
