x^4 + 2x^3 - 4x^2 - 8x + ax^2 + 4ax + 4a
x4+2x3−4x2−8x+ax2+4ax+4a=x3(x+2)−4x(x+2)+a(x+2)2=(x3−4x)(x+2)+a(x+2)2=x(x+2)2(x−2)+a(x+2)2=(x+2)2(x2−2x+a)
Thank you!