(-x^4+x^3-x+1)/(x^2-x+1) =-(x^4-x^3+x-1)/(x^2-x+1) =-[x(x^3+1)-(x^3+1)](x^2-x+1) =-(x-1)(x^3+1)/(x^2-x+1) =-(x-1)(x+1)(x^2-x+1)/(x^2-x+1) = -(x-1)(x+1) = (1-x)(1+x)