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:)
