Bonsoir,
1)
A = (2x + 5)² + (2x + 5) (x - 1)
A = (2x + 5) + (2x + 5 + x - 1)
A = (2x + 5) (2x + x + 5 - 1)
A = (2x + 5) (3x + 4)
2) Pour x = - 2,5
A = (2x + 5) (3x + 4)
A = (2 * (- 2,5) + 5) (3 * (- 2,5) + 4)
A = (- 5 + 5) (- 7,5 + 4)
A = (0) (- 3,5)
A = 0
3)
A = (2x + 5) (3x + 4) = 0
2x + 5 = 0 ou 3x + 4 = 0
2x = - 5 3x = - 4
x = - 5/2 x = - 4/3
x = - 2,5