bonjour
(x - 3)² - 4x + 12 + 3x(x - 3) =
(x - 3)² - 4(x - 3) + 3x(x - 3) =
(x - 3)(x - 3) - 4(x - 3) + 3x(x - 3) = [ (x - 3) facteur commun) ]
(x - 3) [ (x - 3) - 4 + 3x ] =
(x - 3) (x - 3 - 4 + 3x) =
(x - 3)(4x - 7)