bonjour
x² = -x + 2 (1)
(1) <=> x² + x - 2 = 0
<=> x² - 1 + x - 1 = 0
(x² - 1) + (x - 1) = 0 [x² - 1 = x² - 1² ]
(x + 1)(x - 1) + (x - 1)*1 = 0 (on factorise a² - b² = ....)
(x + 1)(x - 1) + (x - 1)*1 = 0 facteur commun (x - 1)
(x - 1)(x + 1 + 1) = 0
(x - 1)(x + 2) = 0 équation produit nul
x - 1 = 0 ou x + 2 = 0
x = 1 x = -2
S = {-2 ; 1}
