Bài làm :
`x^4−3x^3−x+3`
`=x^4−x^3−2x^3+2x^2−2x^2+2x−3x+3`
`=x^3(x−1)−2x^2(x−1)−2x(x−1)−3(x−1)`
`=(x^3−2x^2−2x−3)(x−1)`
`=(x^3+x^2+x−3x^2−3x−3)(x−1)`
`=(x^2+x+1)(x−3)(x−1)`
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`x^2y^2(y−x)+y^2z^2(x−y)−z^2x^2(z−x)`
`=−x^2y^2(x−y)+y^2z^2(x−y)−z^2x^2(z−x)`
`=(y^2z^2−x^2y^2)(x−y)−z^2x^2(z−x)`
`=y^2(z^2−x^2)(x−y)−z^2x^2(z−x)`
`=[y^2(z+x)(x−y)−z^2x^2](z−x)`