bonjour
f (x) = - 2 x² + 12 x +8
f (3)= -2 * 3² + 12*3 + 8 = - 9 + 36 + 8 = 35
2) - 2 x² + 12 x + 8 = 8
- 2 x² + 12 x + 8 - 8 = 0
- 2x ( x - 12 ) = 0
x = 0 ou 12
A (1) = - 2 + 12 + 8 = 18 donc A ∈ C
B ( - 3 ) = - 2 *9 + 12*-3 + 8 = - 18 - 36 +8 = - 46 donc B ∉ C
