bjr
le plus simple
(3x+1)² - 25 = (3x+1)² - 5² = (3x+1 + 5) (3x+1 - 5) = (3x+6) (3x-4) = 3(x+2) (3x-4)
x² - 15x + 14
reprends ton cours pour les formules de calcul..
Δ = (-15)² - 4*1*14 = 225 - 56 = 169 = 13²
x' = (15 +13) / 2 = 14
x'' = (15-13) / 2 = 1
=> x - 15x + 14 = (x - 14) (x-1)
