2x^4-5x^3+x^2-5x+2
= 2(x^4 + 1) - 5x(x^2 + 1) + x^2
= 2(x^2 + 1)^2 - 5x(x^2 + 1) - 3x^2
= {2(x^2 + 1) + x}{(x^2 + 1) - 3x}