x^4+ 1992 x^2 + 1991x + 1992=(x^4+ 1991x)+(1992 x^2 + 1992)=x(x^3+ 1991x)+1992(x^2+1)=(x+1991)(x^3+1991)(x^2+1)=(x^3+1991)(x^2+1)(x+1991)
x^4+ 1992 x^2 + 1991x + 1992=(x^4+ 1991x)+(1992 x^2 + 1992)=x(x^3+ 1991x)+1992(x^2+1)=(x+1991)(x^3+1991)(x^2+1)=(x^3+1991)(x^2+1)(x+1991)