Explications étape par étape:
1)
B(x) = 9x² - 24x + 16 + 9x² - 16 = 18x² - 24x
2)
9x² - 16 = (3x + 4)(3x - 4)
B(x) = (3x - 4)(3x - 4 + 3x + 4) = (3x - 4)×6x = 6x(3x - 4)
3)
B(-3) = (18 × (-3)²) - (24 × (-3))
= 18 × 9 + 72 = 162 + 72 = 234
ou: B(-3) = (6 × (-3))(3 × (-3) - 4
= -18 (-9 -4)
= -18 × (- 13) = 234