Réponse:
A= (x+1)^2 + (x+1)(3x+1)
= (x+1)(x+1)+(x+1)(3x+1)
= (x+1)(x+1+3x+1)
= (x+1)(4x+2)
B= (2x+1)^2+(2x+1)(x+3)
= (2x+1)(2x+1)+(2x+1)(x+3)
= (2x+1)(2x+1+x+3)
= (2x+1)(3x+4)
C= (x-3)^2-(x-3)(4x+1)
= (x-3)(x-3)-(x-3)(4x+1)
= (x-3)(x-3-4x-1)
= (x-3)(-3x-4)
