Question

Descompuneti in factori : (3x+1)(la a doua ) -(x+3)(la a doua) Vreau explicatie !

Answer 1

(3x+1)²-(x+3)²=
9x²+6x+1-(x²+6x+9)=
9x²+6x+1-x²-6x-9=
8x²-8= 8(x²-1)

Answer 2

$(3x+1)^2-(x+3)^2=[(3x+1)-(x+3)][(3x+1)+(x+3)]= \\ =(3x+1-x-3)(3x+1+x+3)=(2x-2)(4x+4)= \\ =8(x-1)(x+1)$