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.