Réponse :

bonjour,

5x(x+7)

5x × x + 5x × 7

= 5x²+ 35

(x+9)(5x+1)

=x × 5x + x ×1 + 9 × 5x + 9×1

= 5x² + x + 45x + 9

=5x² +46x + 9

(3x-2)(6x-4)

= 3x × 6x - 4× 3x - 2 × 6x - 2 ×(-4)

= 18x²-12x -12x+8

= 18x²-24x + 8

(2x+5)(4x-6)-3x (4x-8)

= 8x²-12x + 20x - 30 - ( 12x² -24x )

=8x² + 8x - 30 - 12x² + 24x

= -4x²+ 32x - 30

-2y (3-y)

= -2y × 3 - -2y × (-y)

= -6y + 2y²

voila:)