Le 9,10,11 et 12 svp

9)
a) (x + 4) (x + 2)
= x² + 2x + 4x + 8
= x² + 6x + 8

b) (x + 2) (0,5 + x)
= 0,5x + x² + 1 + 2x
= x² + 2,5x + 1

10)
a) (- 2 + t) (t + 4)
= - 2t - 8 + t² + 4t
= t² + 2t - 8

b) (2t + 5) (5t + 1)
= 10t² + 2t + 25t + 5
= 10t² + 27t + 5

11)
a) (1/2a + 1) (a + 1/2)
= 1/2a² + 1/4a + a + 1/2
= 1/2a² + 1/4a + 4/4a + 1/2
= 1/2a² + 5/4a + 1/2

b) (- 4 + 2a) (- 2 + 5a)
= 8 - 20a - 4a + 10a²
= 10a² - 24a + 8

12)
A = (5x - 4) (1 + 6x)
A = 5x + 30x² - 4 - 24x
A = 30x² - 19x - 4