Bonjour
1) Développer et réduire D.
D = (12x + 3) (2x - 7) - (2x - 7)²
D = 24x² - 84x + 6x - 21 - (4x² - 28x + 49)
D = 24x² - 84x + 6x - 21 - 4x² + 28x - 49
D = 24x² - 4x² - 84x + 6x + 28x - 21 - 49
D = 20x² - 50x - 70
2) Factoriser D.
D = (12x + 3) (2x - 7) - (2x - 7)²
D = (2x - 7) [(12x + 3) - (2x - 7)]
D = (2x - 7) (12x + 3 - 2x + 7)
D = (2x - 7) (10x + 10)
D = 10 (x + 1) (2x - 7)
3) Calculer D pour x = 2 et x = -1.
D = 20x² - 50x - 70
D = 20 * 2² - 50 * 2 - 70
D = 20 * 4 - 100 - 70
D = 80 - 170
D = 90
D = 20x² - 50x - 70
D = 20 * (- 1)² - 50 * (-1) - 70
D = 20 * 1 + 50 - 70
D = 20 + 50 - 70
D = 70 - 70
D = 0.