bonsoir
5 x - 7 < 9
5 x < 9 + 7
5 x < 16
x < 16/9
] - ∞ ; 16/9 [
3 x + 7 < 9 x + 4
3 x - 9 x < 4 - 7
- 6 x < - 3
x > 3/6 = 1 /2
] 1/2 : + ∞ [
( 7 x - 4 ) ( 5 x + 4 ) ≤ 0
7 x - 4 ≤ 0
7 x ≤ 4
x ≤ 4/7
5 x + 4 ≤0
5 x ≤ - 4
x ≤ - 4 /5
[ - 4/5 ; 4/7 ]
continue