Explications étape par étape :
(x - 3 ) ( 2x + 1 ) ≤ ( 5 - x ) ( 2x + 1 )
2x² + x - 6x - 3 ≤ 10x + 5 - 2x² - x
2x² - 5x - 3 ≤ -2x² + 9x + 5
4x² - 14x - 8 ≤ 0
2x² - 7x - 4 ≤ 0 ( /2 )
Δ = (-7)² - 4 . 2 (-4)
⇔ Δ = 49 + 32 = 81
Δ > 0
x₁ = ( 7 - √81 ) / 4 = -2/4 = -1/2
x₂ = ( 7 + √81 ) / 4 = 16/4 = 4
S = [ -1/2 ; 4 ]
