(a) x²+5x+1=0, Δ=21, x=(-5±√(21))/2
(b) 2x²-10x+3=0, Δ=76=(2√19)², x=(10±2√19)/2 = 5±√19
(c) -x²+3x-1=0, Δ=5, x=(-3±√5)/2
(a) x² + 5x + 1 ≤ 0 sur [(-5-√(21))/2 ; (-5+√(21))/2]
(b) 2x² – 10x + 3 ≥ 0 sur R\]5-√19 ; 5+√19[
(c) –x² + 3x – 1 ≥ 0 sur [(-3-√5)/2 ; (-3+√5)/2]