1/
(x+3)(4x-12) -(x-3)² =0

2/

(4x-12)

4(x-3)

3/

(x+3)(4x-12)-(x-3)² =0

4(x+3)(x-3) -(x-3)²=0

(x-3)(4x+12-x+3) =0

(x-3)(3x+15)=0

x-3 =0                                    3x+15 =0

x =3                                          3x = -15

x=3                                              x = -15/3

donc antecedent (3 ; -15/3)