bjr
x² + 4x - 21 = 0
Δ = 4² - 4*1*(-21) = 16 + 84 = 100 = 10²
x' = (-4 +10) / 2 = 3
x'' = (-4-10)/2 = -7
=> x² + 4x - 21 = (x-3) (x+7)
8x² + 8x + 2 = 0
Δ = 8² - 4*8*2 = 64 - 64 = 0
donc deux solutions semblables
x' = x" = -8/2*8 = -0,5
8x² + 8x + 2 = 8 (x + 0,5) (x + 0,5)
-3x² + 7x - 8 = 0
Δ = 7² - 4*(-3)*(-8) = 49 - 96 =>
Δ < 0
pas de solution de factorisation