bonsoir

(3 x + 1 )² - 4

= ( 3 x + 1 - 2 ) ( 3 x + 1 + 2 )

= ( 3 x - 1 ) ( 3 x + 3 )

= 3 ( 3 x - 1 ) ( x + 1 )

(3x - 1)(3x + 3) = 0

x =  1/3 ou - 3/3 = - 1