$P(x)=x^3+3x^2+3x-2$
$Q(x)=-x^3-x^2-5x+2$
$+,P(x)+Q(x)=x^3+3x^2+3x-2-x^3-x^2-5x+2$
$P(x)+Q(x)=2x^2-2x$
$+, P(x)-Q(x)=x^3+3x^2+3x-2-(-x^3-x^2-5x+2)$
$P(x)-Q(x)=x^3+3x^2+3x-2+x^3+x^2+5x-2$
$P(x)-Q(x)=2x^3+4x^2+8x-4$
$H(x)=Q(x)+P(x)$
$2x^2-2x=0$
$2x(x-1)=0$
$+,x=0$
$+,x-1=0$
$x=1$
Vậy `x∈{0,1}` là nghiệm đa thức $H$