bonsoir
B (x) = - 15 x² + 6 x + 15 x² - 6 x + 40 x - 16
B (x) = 40 x - 16
B (x) = ( - 5 x + 2 ) ( 3 x - 3 x - 8 )
B (x) = ( - 5 x + 2 ) ( - 8 )
B (x) = 0 pour - 5 x + 2 = 0 ⇔ - 5 x = - 2 ⇔ x = 2/5
