bonjour

9 x² - 49  ⇒ identité remarquable , différence de 2 carrés

= ( 3 x - 7 ) ( 3 x + 7 )

E =  9 x²  - 49 - ( 3 x - 7 ) ( 2 x  - 1 )

= ( 3 x - 7 ) ( 3 x + 7 ) - ( 3 x - 7 ) ( 2 x  - 1 )

= ( 3 x  - 7 ) ( 3 x + 7 - 2 x + 1 )

= ( 3 x - 7 ) ( x + 8 )

F = 6 x - 21 + ( 2 x - 7 ) ( 1 - 5 x )

= 3  ( 2 x  - 7) + ( 2 x  - 7 ) ( 1 - 5 x )

= ( 2 x - 7 ) ( 3 + 1 - 5 x )

= ( 2 x - 7 ) ( - 5 x + 4 )

Bonjour,

1) 9x² - 49 = (3x - 7) (3x + 7)

E = 9x² - 49 - (3x - 7) (2x + 1)

E = (3x - 7) (3x + 7) - (3x - 7) (2x - 1)

E = (3x - 7) [(3x + 7) - (2x - 1)]

E = (3x - 7) (3x + 7 - 2x + 1)

E = (3x - 7) (x + 8)

2) 6x - 21 = 3 (2x - 7)

Donc :

F = 6x - 21 + (2x - 7) (1 - 5x)

F = 3 (2x - 7) + (2x - 7) (1 - 5x)

F = (2x - 7) (1 - 5x + 3)

F = (2x - 7) (- 5x + 4).