Răspuns :
Se foloseste formula [tex] x^{2} - y^{2} =(x-y)(x+y)[/tex] si obtinem 4(x+2)(2x+3)
[tex](3x+5)^2-(x+1)^2=[(3x+5)-(x+1)][(3x+5)+(x+1)]= \\ =(3x+5-x-1)(3x+5+x+1)=(2x+4)(4x+6)= \\ =2(x+2) \cdot 2(2x+3)=4(x+2)(2x+3)[/tex]