a) ( x+ 3 ) ( x - 3 ) = 3 ( x-3)
x+ 3 =3
x =0
a) x2 - 9 = 3( x - 3 )
⇔ ( x - 3 )( x + 3 ) - 3( x - 3 ) = 0
⇔ ( x - 3 )( x + 3 - 3 ) = 0
⇔ ( x - 3 ).x = 0
⇔ x - 3 = 0 hoặc x = 0
⇔ x = 3 hoặc x = 0
b) 3( 3x2 + 1 ) = 6 - 2( 3x + 2 )
⇔ 9x2 + 3 = 6 - 6x - 4
⇔ 9x2 + 6x + 3 - 6 + 4 = 0
⇔ 9x2 + 6x + 1 = 0
⇔ ( 3x + 1 )2 = 0
⇔ 3x + 1 = 0
⇔ x = -1/3