Bonjour,
1 ) A(x) = (3x - 5)² + (x + 3) (3x - 5)
A(x) = 9x² - 30x + 25 + 3x² - 5x + 9x - 15
A(x) = 12x² - 26x + 10
2) A(x) = (3x - 5) (3x - 5 + x + 3)
A(x) = (3x - 5) (4x - 2)
A(x) = 2 (3x - 5) (2x - 1)
3) A(x) = 0 ⇔ 3x - 5 = 0 ou 2x - 1 = 0
⇔ x = 5/3 ou x = ½