因式分解x^4+1991x^2+1990x+1991

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因式分解x^4+1991x^2+1990x+1991
因式分解x^4+1991x^2+1990x+1991

因式分解x^4+1991x^2+1990x+1991
答:
x^4+1991x^2+1990x+1991
=(x^4-x)+1991(x^2+x+1)
=x(x^3-1)+1991(x^2+x+1)
=x(x-1)(x^2+x+1)+1991(x^2+x+1)
=(x^2-x+1991)(x^2+x+1)