Réponse:
A=5x ×(3x+7)
A=5x ×3x+5x ×7
A=15x²+35x
B=(5_2x)×(3x+7)
B=5×3x+5×7-2x ×3x-2x ×7
B=15x+35-6x²-14x
B=x+35-6x²
B=-6x²+x+35
