(x^2+2x+1)*(x^2+2x)=12
x^4+2x^3+4x^2+x^2+2x=12
x^4+4x^3+5x^2+2x=12
x^4+4x^3+5x^2+2x-12=0
x^4-x^3+5x^3-5x^2*(x-1)+10x*(x-1)+12(x-1)=0
(x-1)*(x^3+5x^2+10x+12)=0
(x-1)*(x^3+3x^2+2x^2+6x+4x+12)=0
(x-1)*(x^2*(x+3)+2x*(x+3)+4(x+3))=0
(x-1)*(x+3)*(x^2+2x+4)=0
x-1=0
x+3=0
x^2+2x+4=0
x=1
x=-3
Ответ: x1=-3; x2=1