=(x4+x2+1)+(1996x2+1996x+1996)
=(x2+x+1)(x2-x+1)+1996(x2+x+1)
=(x2+x+1)(x2-x+1+1996)
\(x^4+1997x^{ 2}+1996x+1997\)
\(=\left(x^4-x\right)+\left(1997x^2+1997x+1997\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+1997\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left[x\left(x-1\right)+1997\right]\)
\(=\left(x^2+x+1\right)\left(x^2-x+1997\right)\)