Réponse :
Bonjour
A = (2x + 3)² - (5x - 3)(4x + 7)
A = ((2x)² + 2 × 2x × 3 + 3²) - (5x × 4x + 5x × 7 - 3 × 4x - 3 × 7)
A = 4x² + 12x + 9 - (20x² + 35x - 12x - 21)
A = 4x² + 12x + 9 - (20x² + 23x - 21)
A = 4x² + 12x + 9 - 20x² - 23x + 21
A = - 16x² - 11x + 30
2) x = 2
A = - 16 (2)² - 11(2) + 30
A = - 16 (4) - 22 + 30
A = - 64 + 8
A = - 56
