Bonjour,
a. B = (3x + 4)² - 81
B = 9x² + 24x + 16 - 81
B = 9x² + 24x - 65
b. B = (3x + 4)² - 81
B = (3x + 4 - 9) (3x + 4 + 9)
B = (3x - 5) (3x + 13)
c. Pour x = - 5
B = 9x² + 24x - 65
B = 9 * (- 5)² + 24 * (- 5) - 65
B = 9 * 25 - 120 - 65
B = 225 - 185
B = 40
Pour x = 5/3
B = 9x² + 24x - 65
B = 9 * (5/3)² + 24 * (5/3) - 65
B = 9 * 5²/3² + 120/3 - 65
B = 9 * 25/9 + 40 - 65
B = 225/9 - 25
B = 25 - 25
B = 0
d. B = 0
B = (3x - 5) (3x + 13) = 0
3x - 5 = 0 ou 3x + 13 = 0
3x = 5 3x = - 13
x = 5/3 x = - 13/3.
