Bonjour,
1) E = (3x + 5)² - (3x + 5) (x + 8)
E = 9x² + 30x + 25 - (3x² + 24x + 5x + 40)
E = 9x² + 30x + 25 - 3x² - 24x - 5x - 40
E = 9x² - 3x² + 30x - 24x - 5x + 25 - 40
E = 6x² + x - 15
2) E = (3x + 5)² - (3x + 5) (x + 8)
E = (3x + 5) [(3x + 5) - (x + 8)]
E = (3x + 5) (3x + 5 - x - 8)
E = (3x + 5) (2x - 3)
3) E = (3x + 5) (2x - 3) = 0
3x + 5 = 0 ou 2x - 3 = 0
3x = - 5 2x = 3
x = - 5/3 x = 3/2
4) E = 6x² + x - 15
E = 6 * 3/2² + 3/2 - 15
E = 3 * 3²/2² + 3/2 - 15
E = 3 * 9/4 + 3/2 - 15
E = 27/4 + 6/4 - 60/4
E = - 27/4
E = - 6,75.
