由（x^4-x²-4x-4)/(x-2)(x+1)=[x²(x²-1)-4(x+1)]/(x-2)(x+1)=[x²(x-1)(x+1)-4(x+1)]/(x-2)(x+1)=(x+1)(x³-x²-4)/(x-2)(x+1)=(x+1)(x-2)(x²+x+2)/(x-2)(x+1)=x²+x+2.