Bonjour,
1) Développer :
M = (3x + 5)² - (3x + 5) (2x + 7)
M = 9x² + 30x + 25 - (6x² + 21x + 10x + 35)
B = 9x² + 30x + 25 - 6x² - 21x - 10x - 35
B = 9x² - 6x² + 30x - 21x - 10x + 25 - 35
B = 3x² - x - 10
2) Factoriser :
M = (3x + 5)² - (3x + 5) (2x + 7)
M = (3x + 5) [(3x + 5) - (2x + 7)]
M = (3x + 5) (3x + 5 - 2x - 7)
M = (3x + 5) (x - 2)
3) Calculer M pour x = - 5/3
M = 3x² - x - 10
M = 3 * (- 5/3)² - (- 5/3) - 10
M = 3 * (25/9) + 5/3 - 10
M = 75/9 + 15/9 - 90/9
M = 90/9 - 90/9
M = 0
4) Résoudre M = 0
M = (3x + 5) (x - 2) = 0
3x + 5 = 0 ou x - 2 = 0
3x = - 5 x = 2
x = - 5/3.
