Bonjour,
On donne A = (5x+2)² - (3x-7)(5x-2)
1) Développe et réduis A
A = (5x+2)² - (3x-7)(5x-2)
A = 25x² + 20x + 4 - (15x² - 6x - 35x + 14)
A = 25x² + 20x + 4 - 15x² + 6x + 35x - 14
A = 25x² - 15x² + 20x + 6x + 35x + 4 - 14
F = 10x² + 61x - 10
2) Factorise A
A = (5x+2)² - (3x-7)(5x-2)
A = (5x + 2) [(3x - 7) - (5x - 2)]
A = (5x + 2) (3x - 7 - 5x + 2)
A = (5x + 2) (- 2x - 5)
3) Résous l’équation A =0
A = (5x + 2) (- 2x - 5)
5x + 2 = 0 ou - 2x - 5 = 0
5x = - 2 - 2x = 5
x = - 2/5 x = - 5/2
