bonsoir
A (x) = ( 3 - x ) ( 5 - 2 x ) > 0
3 - x = 0 ⇔ - x = - 3 ⇔ x = 3
5 - 2 x = 0 ⇔ - 2 x = - 5 ⇔ x = 5/2
tu fais le tableau de signes
S ] - ∞ ; 5/2[ ∪ ] 3 ; + ∞ [
B (x) = x ( 2 x + 1 ) ≤ 0
x = 0
2 x + 1 = 0 ⇔ 2 x = - 1 ⇔ x = - 1/2
S [ -1/2 ; 0 ]
C(x) = ( x + 7 ) / 2 x - 3 < 0
x + 7 = 0 ⇔ x = - 7
2 x - 3 = 0 ⇔ 2 x = 3 ⇔ x = 3/2 = valeur interdite
S ] - 7 ; 3/2 [
